Mic Kaczmarczik`s Qanda Information

Transcript

Mic Kaczmarczik's qanda Information Mic Kaczmarczik's qanda Information This directory contains USENET articles Mic has saved about guitars, equipment, pickup, techniques, players, and so on. Mic has graciously granted permission to post the stuff on the JT30 page on the off chance that it might be useful in the context of Blues Harmonica. Mic is not responsible for the content, just the collection. Dealer Cost Vs List Price Death Switch Dont Use Stereo Speakers Effects FAQ.1 Effects FAQ.2 Effects FAQ.3 Fix Reverb Ground Hum Flea Market Checkout Hammond Organ Buys Hammond Tonewheel Organs How Long Do Tubes Last How Many Watts Magnetics for Morons Microphone Placement NOS defined Stage Placement What Are Optoisolators What Dealers Pay What Is Tube Glow What JBL Means What are orange drops What is 6V6GTA What is Bias What is Blue Glow What is Ground Lift What is Kinkless Tetrode What is Single Ended What is a Fetron What is a Klystron What is a Plexi Which 4x12 Impedance Who Made Delco Tubes Who Makes Kendrick Spkrs Why 16ohm Loads Why AC on heaters Why Blackface an Amp Why Bleeder Resistors Why Cap Value Spread Why Care About Phase Why Change SF Lead Dress Why Microphonic Cords Why Not Bias By Scope Why Opto Trem Why Select Highest Z Tap Why Sprague Caps Why Use Grid Stoppers Why Use Standby Why rectifier is separate Dealer Cost Vs List Price Dealer Cost Vs List Price From [email protected] Sun Oct 24 10:42:22 CDT 1999 From: [email protected](Lord Valve) Newsgroups: alt.guitar.amps Subject: Re: Company Muscle Re: PRICE MISQUOTE ON MESA TUBES (SEE CORRECTION) Date: 23 Oct 1999 06:00:24 GMT Xref: geraldo.cc.utexas.edu alt.guitar.amps:210511 In <[email protected]> [email protected] (DEidelberg) writes: > >>>(I forget the real >number, but the dealer discount was something on the order of 30% or so)... >My friend's amp was ready a few days after, and when he went to the factory >pick it up, he was approached by T.L. who was apparently quite upset and >told my friend that he had done the company a "great disservice." My friend >was pissed as hell, as you can imagine, and that was the last time he dealt >with Boogie for any reason.<< > >Why was your friend pissed off? He saw some confidential information while >"buzzing around the factory." Then he disclosed this information to the >public. T.L. had reason to be pissed off. > >By the way, even if the dealer cost was 30% off list (don't forget to add >shipping and overhead for the store), that profit margin really isn't bad at >all. Most of the music gear goes to dealers at 50% off list. Lord Valve Speaketh: Lots of people in the retail trades make a big deal out of "protecting" dealer price lists and such. That's where codewords like "keystone" and the like came from. My take on it is this: I don't give a rat's ass if anyone knows what my cost on an item is; they are free to buy or not to buy as they choose. Many musicians, for instance, have no idea that strings can be had on the wholesale level for as little as 20 cents on the dollar. (This means that a set of strings which retails for ten bucks only costs the dealer two.) In this case, the dealer can offer the customer a half-price "special," where two sets of strings are sold for the retail price of one set. On its face, this looks like a great deal for the consumer, but in actuality the dealer is taking in 2-1/2 times his cost. Of course, this is an extreme example; a *large* number of sets must be purchased for the dealer to obtain this much of a discount, and that pretty well limits deals like this to the megabucks outfits like Guitar Center, Musician's Friend, etc. Some items (Mesa amps, for instance) don't carry a large markup. Mesa's discount schedule is 25% on some items, 30% on others. Behringer stuff is 50% (keystone) as is QSC. Other lines (like Studiomaster) have different schedules for different items; the higher-end recording consoles carr a 40% discount, while the low-end mixers go for 50% of retail. Sometimes the net price to the dealer depends on how quickly the invoice is settled...the invoice terms may be "10%/30, net/31." This means that if the dealer pays the invoice in 30 days or less, a 10% additional discount is applied to the total. A $100 item may have an invoice price of $60, with a 10% discount for prompt payment; this puts the net price for the item at $54, which is a 46% discount from retail. Many dealers will split the markup with the customer by offering a 23% discount on the item. Customer's price = $77, dealer's profit = $23, which is a decent markup. I don't know why they don't teach this stuff in the third grade; many people have no idea how business is actually done. This probably accounts for the 90% small-business failure rate. At any rate, if anyone wants to know the discount schedule for anything, I'll be glad to tell you if I have the info. It's not like selling missile secrets to the Chinese, for pete's sake. Lord Valve VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NBS Electronics, 230 South Broadway, Denver, CO 80209-1510 Phone orders/tech support after 1:00 PM Denver time at 303-778-1156 NOW ACCEPTING VISA AND MASTERCARD CHAT WITH LORD VALVE: Log onto any DALnet server and join channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. "It ain't braggin', if ya can do it." - Babe Ruth Death Switch Death Switch From [email protected] Thu Jun 8 17:33:11 CDT 1995 From: [email protected] (Dr Distortion) Newsgroups: alt.guitar.amps Subject: Re: Death switch. Date: 8 Jun 1995 17:46:23 GMT Mark Garvin ([email protected]) wrote: : 2. Break the shielding from the guitar cable going to amp #2. Assuming both amps have grounded AC outlets, that's the best and easiest way. I would never try to float the ground at the outlet. : 3. Make sure both amps' ground switches (death switches) are : disabled. : In any event, the ground (death) switch is just one incredible : invention. How many toasty guitarists result? I hate that stupid fuckin' switch, and I remove it from all my amps. I also remove any fixed (unswitched) "grounding" caps that may be present >from the AC line to the chassis. I got bit by my share of hot chassis in my pre-technical gigging days, when I didn't know about that cap going to the chassis. If I do end up using an amp equipped with the "death" cap (like if I'm using someone else's amp), I check between the chassis and earth ground with a multimeter set to AC volts. I adjust the switch or the plug orientation for the lowest voltage (usually 1-2 volts if the cap is going to the neutral line). Dont Use Stereo Speakers Dont Use Stereo Speakers From [email protected] Fri May 12 09:12:27 CDT 2000 From: Lord Valve Newsgroups: alt.guitar.amps Subject: Re: Speaker Failure II Date: Thu, 11 May 2000 23:45:37 -0600 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Server-Date: 12 May 2000 05:43:18 GMT Xref: geraldo.cc.utexas.edu alt.guitar.amps:250420 Lord Valve Speaketh: My two-word answer was based on thirty years of experience. I've seen mountains of smoked home stereo speakers that were used for guitar amps. I've also seen piles of fricasseed homestereo equipment that cheapass bar-owners tried to use for playing tunes in their bars. Home stereo speakers are built with compressed program material in mind...they are for *playback* of recorded material, not for amplification/reinforcement of *live* (uncompressed) electric/electronic instruments. They are also designed to produce a limited soundfield; when used in large rooms, they are easily overdriven. Voice-coil wattage ratings, suspension components, box design, crossover components...all are picked with regard to use for playback of recorded program material when home stereo speakers are designed. Transients produced by live instruments that are routinely handled by MI speakers can *destroy* home stereo speakers in milliseconds. The "first hand experience" I have with this mostly consists of laughing when someone comes into my repair department carrying a home stereo speaker that they fried by playing the guitar through it. Usually they say, "Hey, it says it's rated at 200 watts on the back of the cabinet. My reciever is only 60 watts a channel, so why did it blow?" It blew, junior, because you misused it. If you use a Coke bottle when what you actually need is a hammer, you'll wind up with a busted bottle. Period. Lord Valve VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NBS Electronics, 230 South Broadway, Denver, CO 80209-1510 Phone orders/tech support after 1:00 PM Denver time at 303-778-1156 NOW ACCEPTING VISA AND MASTERCARD CHAT WITH LORD VALVE: Log onto any DALnet server and join channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. I AM filthy rich, but my wealth has all been stolen and the Russian Military has it all very well documented, recorded, that is the TRUTH! As long as any American is allowed to be filthy rich, I want every cent of MY MONEY, too, so I can use it to educate fools as to why they should be smart enough to never, ever, let anyone to be rich again! - Nancy Luft MindSpring User wrote: > Lord Valve, > I think my reply to Ron Sonic fits your answer too. I'm truely seeking first > hand accounts of equipment failure. I've read many of your posts and am > honored to you're weigh in on my mine but it's not what I'm looking for. > Dave M. Effects FAQ.1 Effects FAQ.1 From [email protected] Sun Dec 18 11:35:48 CST 1994 From: [email protected] (RGKeen) Newsgroups: alt.guitar Subject: Guitar Effects FAQ 1/3 Date: 18 Dec 1994 10:46:04 -0500 Sender: [email protected] Reply-To: [email protected] (RGKeen) Guitar Effects FAQ Version 2.01, 15 December 1994 rec.music.makers.builders rec.music.makers.guitar alt.guitar This FAQ was created by R.G. Keen, [email protected] Last update 15 December 1994 [the faq is split into three pieces because my !@#!@# aol software can't accept the file as big as it is. sorry. I'm looking for another service.] This is section 1 of 3. =========================================================================== INDEX: Introduction Contributors What kinds of effects are there? amplitude based effects waveform distortion effects filter/frequency response effects time delay effects other miscellaneous effects common combinations Answers to questions about terminology Difference between overdrive and distortion Difference between vibrato and tremolo Where can I find schematics for guitar effects? Books Magazines Kits The Net How practical is building your own effect? Skills and tools for building effects Effects Packaging Procuring Parts Recommended suppliers are: Answers to questions about fixing broken effects Completely dead pedal Sound, no delay in older delay pedals Scratchy Wah Pedal Appendix A - Effects Economics 101 Appendix B - Making Circuit Boards Appendix C - My Personal Best Way to Package Effects Appendix D - A Musical Distortion Primer ========================================================================== INTRODUCTION This FAQ is a generic answer to the questions which begin: I have heard of an effect called a DoWhizzer. What is this? "My Phaser/Blaster/Clinker pedal is acting funny/dead. Can this be fixed/how can I fix this? "I have some electronics abilities and I'd like to build my own guitar effects. Where can I find schematics for this?" I have done this for a long time, so I thought I'd write down some facts and some of my opinions. I have tried to weed out a lot of possible-but-difficult things in writing this. Where I simply state that something ought to be done some way, this is usually an opinion based on having tinkered. My opinion is subject to being wrong at times, so if you know a better way, or if I have left out something that is much simpler and easier, let me - and the rest of us - know. I certainly won't be offended at having a mistake pointed out. If you have something to contribute along these lines, by all means, send it to me or post it. ========================================================================== CONTRIBUTORS: Many thanks to those of you who have sent additions and corrections including: David Mourning Murray Traue Jamie Heilman [email protected] Scott Lehman ========================================================================== What kinds of effects are there? Effects are usually based on some facet of the human ear's abilities to figure out from amplitude and frequency content variations what a sound source is doing. This was critical when the sound source might be a saber toothed tiger. Now it is a means for us to express ourselves musically by directly invoking emotion. I tried to count up all of the things I could think of that an effect could even possibly be based on. The raw list is stated first, just as a reference, and afterwards I give a short definition of each effect. Since distortion is perhaps the most musically interesting effect to a guitarist, I also include a primer on distortion and an exhausting ...er... exhaustive (to me at least) list of ways to get musically useful distortion in Appendix D. AMPLITUDE BASED EFFECTS These are all based on the instantaneous loudness of the signal, how it changes, and how quickly it changes. Volume control Tremolo Auto tremolo Panning/ping-pong Gating/repeat percussion Compression Expansion Asymmetric compression/peak compression Noise gating Attack delay ADSR Limiting Auto swell WAVEFORM DISTORTION EFFECTS All the generic ways to distort the waveform that comes from the guitar. Symmetrical clipping Asymmetrical clipping Infinite limiting Half wave rectification Full wave rectification Arbitrary waveform generation FILTER/FREQUENCY RESPONSE EFFECTS EQ/tone controls Treble/mid/bass boost Cabinet simulation Resonator Wah Auto wah Tremolo-wah "vibrato" Phase shifting TIME DELAY EFFECTS Reverb Echo True vibrato Flanging Chorus/ADT Slapback Reverse echo/reverb Sampling? OTHER MISCELLANEOUS EFFECTS Octave division Harmony generation Phase lock tracking Noise addition Talk box Voice tracking (vocoder) Ring modulation (DSBSC generation) SSBSC generation COMMON COMBINATIONS Leslie (vibrato, tremolo, varying filtering generated by rotating speaker) Aphex (filtering, selective frequency band distortion) EFFECTS DESCRIPTIONS ==================== AMPLITUDE BASED EFFECTS Volume control Manual level control. Twist the knob, the sound gets louder or softer. Tremolo cyclical variation of volume by a low frequency oscillator of some sort; parameters are waveform of the LFO, LFO frequency, and depth of modulation; note that while the terms tremolo and vibrato are often used interchangeably, tremolo is actually variation in loudness, vibrato is variation in pitch or frequency. Auto tremolo tremolo where the modulation frequency is varied by some feature of the input signal, generally amplitude. Panning/ping-pong generalization of tremolo to more than one channel; as one channel goes down in level, another goes up. With non-square LFO waveforms, gives the effect of the sound source moving from place to place in stereo or more channel setups. Gating/repeat percussion tremolo with 100% modulation of the signal by a square wave. With exponentially decaying waveforms (guitar is a good one), gives the effect of striking the same note again at decreasing levels. Some Thomas Organ Vox amps have this as a built in effect. Compression makes soft inputs louder, and loud ones softer, giving a one-level kind of sound with lessened dymanics. This is effectively volume control with the level determined by the negation of the averaged envelope of the input level. Expansion Makes loud sounds louder and soft ones softer. Effectively volume control with the level determined by the averaged envelope of the input level. Compression and expansion can be complementary, as in com(pression/exp)anding for noise reduction. Asymmetric compression/peak compression Only the peaks of the input waveforms get compressed, not the overall level of the waveform envelope. Effectively, there is no averaging of the envelope and the instantaneous waveform level is compressed. This amounts to a much softer form of clipping, and is part of the tube sound, since tube with a soft B+ supply are prone to this. Noise gating modulates the output off when the input level is below a threshold. The modulation may be a square wave, or a variation of expansion where the low level inputs are "expanded" down into silence, which gives a less abrupt transition. Attack delay A variation of noise gating where the transition to "on" from the "off" or no signal state is slowed. This gives an output which perceptibly rises in level with each new note envelope, reminiscent of a tape recording played backwards. ADSR term borrowed from the synthesizer folks; stands for Attack Decay Sustain Release, which is the most general way to describe a musical envelope. It is possible to generate an artificial ADSR envelope for a musical note to help fool the ear as to which instrument generated the note. Limiting Like compression, but operates on signals over some threshold only. Well suited to keep an input from going over some level, but un-processed below that level, as in getting signals on tape without overloading the tape. Auto swell generally, a rise in level from some starting level to a final level when keyed manually or electronically. Can effectively add sustain to some notes and not others when keyed manually, or can add a "swell" in volume over a run of notes, or can help with presetting the level of a lead. WAVEFORM DISTORTION EFFECTS Symmetrical clipping For a given input waveform, say a sine wave, the tops and bottoms of the waveform are clipped equally, symmetrically. Although the musical implications are more involved than this simplistic explanation, for a simple sine wave, symmetrical clipping generates only odd-order harmonics, giving a reedy, or raspy sound to the resultant waveform. The hardness or softness of the clipping matters. Hard clipping results when the output wave equals the input up/down to a certain level, then stays at the clipping level until the input drops below the clipping level again, giving perfectly flat tops and bottoms to the clipped output. Soft clipping has no abrupt clipping level, but gently rounds the top/bottom of the output wave so the waveform is "softly" rounded on top/bottom, not flat-topped. Some solid state devices actually flat top, then invert, producing a hollow topped output waveform at hard clipping. There is a continuum of clipping hardness, depending on the circuitry used to clip. Soft clipping emphasizes the lower- order harmonics, the third and fifth, etc. Hard clipping has a mix slewed to the higher order seventh and up harmonics, which are harsher sounding. Intermodulation distortion, the production of sum and difference frequencies from frequencies in the input waveform, varies with the amount and hardness of clipping. Intermodulation sounds harsh and ugly. The amount of intermodulation is a characteristic of the circuit that produces the distortion. Asymmetrical clipping The top(or bottom) of the waveform is clipped more than the bottom (top) half. This causes the generation of both even and odd harmonics, in contrast to symmetrical clipping's odd-order only. The even harmonics are smoother and more musical sounding, not as harsh as the odd ones. The hardness of the clipping and the degree of asymmetry affect the sound. The more asymmetrical, the more pronounced the even-order harmonics; the harsher the clipping, the more the harmonics are slewed toward higher order. See Half Wave Rectification. Tubes in general produce asymmetrical distortion unless the circuitry is set up to remove them, as happens in push-pull. The comments on intermodulation apply here. Infinite limiting In essence, the waveform is amplified "infinitely" and hard and symmetrically clipped, producing a rectangular output waveform which shares only the zero crossings with the input waveform. Sounds buzzy and synthesizer-ish. Half wave rectification Half wave rectification represents the logical conclusion of asymmetrical clipping. One half of the waveform is flat, the other half is unchanged. This produces a prominent second harmonic, heard as an octave. There are analog devices which produce an octave effect injust this way; I have heard that the "Octavia" effect is based on this. Full wave rectification In full wave rectification, one half of the input waveform is "folded" to the opposite polarity, producing an output with a net DC component, none of the original fundamental frequency of the input waveform, and only the second and higher harmonics of the original input frequency. Produces very strong octave of the input waveform, as well as a slew of even-, odd-, and intermod- distortion products when more than a single frequency is the input ( as is the case for all musical instruments). Arbitrary waveform generation This effect generates a completely new waveform of arbitrary shape which shares the same frequency as the input waveform. Guitar synthesizers do a version of this. FILTER/FREQUENCY RESPONSE EFFECTS EQ/tone controls Allow you to cut or boost the highs, lows, mids etc. Tend to be broad-brush kinds of controls - all the "high's" get raised or cut. Range is typically +/- 12 to 20 db boost/cut. Treble/mid/bass boost like an additional eq control, but tends to be narrower in frequency range, and perhaps more boost range, no cut. Cabinet simulation A filter network designed to mimic the two- or four-pole low frequency rolloff of a guitar speaker cabinet, usually to get that "miked cabinet" sound into a PA without really miking a cabinet. Resonator a filter with a boost in frequency at a narrow range of frequencies. This sounds like a wah pedal when the pedal is not being moved. Wah A resonator that can have its center frequency moved up or down in frequency by moving a pedal. The "wah" name comes from the way it mimics the moving resonance of the human vocal tract in speech as the sound "wah" is made. Auto wah or "Envelope Follower" A wah filter where the center frequency is determined by the loudness of the input signal, making a moving resonance on every note Tremolo-wah Wah where the center frequency is moved back and forth cyclically, as though the pedal was connected to a motor or some such. This can generate effects similar to a rotating speaker or phasing. "vibrato" a cyclical variation in the basic frequency of the input signal, similar to the effect of moving the whammy bar on a suitably equipped guitar. True vibrato as an add on effect requires some kind of time delay, and was hard to do until analog (and now digital) delays came to be. Phase shifting This effect is a filter response generated by using long phase delays and mixing with the original signal to cause a number of deep notches and/or peaks in the overal filter response. This mimics the larger number of notches and peaks caused by true time delayed flanging. Most simple phase shifters or phasers do this by generating two notches, although some pedals make four notches. Flangers may make many notches. Phasers may also incorporate feedback to sharpen up the effect of the notches. TIME DELAY EFFECTS Echo Reverb True vibrato Flanging Chorus/ADT Slapback Reverse echo/reverb Sampling? OTHER MISCELLANEOUS EFFECTS Octave division Takes the fundamental frequency of an input signal, divides it by two, and creates an octave-lower, sometimes a two-octave lower signal, which are usually mixed back with the original signal. This is most often done with digital logic flipflops to divide the signal by two/four after squaring up the input to drive the flipflops. This provides outputs that are substantially square waves, sounds like fuzz bass. Some kind of filtering is usually provided to tame the sharp buzz of the square waves. The simple dividers like this get very confused when fed more than one tone at once, so single note runs are all that is really practical - unless you like confused effects. Harmony generation Generation of other notes at musically-interesting intervals along with your notes. The classic device to do this is the Eventide Harmonizer. It is very difficult to do this electronically so that the effect produces musically-useful sounds consistently, hence Eventide's high price. Phase lock tracking An electronic circuit called a "phase locked loop" can produce an output signal that is exactly an integer multiple or small-numbers fractions of a reference signal in frequency. You can generate: a signal that follows your notes, perhaps lagging a little with a glide onto the note an octave or two above a third/fifth/seventh, etc. above or below your notes. Sounds kind of like a computer playing harmony with you. The outputs are usually square wave or filtered square wave, and sound kind of synthesizer-y. Modern all-digital MIDI-fied effects do something like this in their computer processors, and may not be as limited in output waveform. Noise addition Noise (hiss, rumble, etc) is deliberately added to the input signal. If this is done with restraint and matching the input signal envelope, it can add a breathing effect like the hiss of air in a flute. Talk box This effect is produced by using a small amp to produce sound that is conducted into your mouth by a tube, so you can mouth the words to a song, using your vocal tract resonances to shape the instrument sound, which is then picked up by a microphone. This is the archetypical "talking guitar". Voice tracking (vocoder) Ring modulation (Double Side Band Suppressed Carrier generation) Single Side Band Suppressed Carrier generation COMMON COMBINATIONS Leslie (vibrato, tremolo, varying filtering generated by rotating speaker) ========================================================================== Answers to questions about terminology Q. What is the difference between "distortion" and "overdrive"? A. Effectively none. "Overdrive" started as what you got when you put too large a signal into the input of an amp, causing the signal to be distorted at the speaker. You were "overdriving" the inputs. "Distortion" is the more generic term, and started when folks noticed that you could get a distorted sound from a little solid state amp that was VERY nonlinear. The terms have been used so interchangeably that there is no real difference, although some people will swear that only tubes being overdriven sound good, etc. Let them insist. It won't hurt much either way. Q. What is the difference between "vibrato" and "tremolo"? A. In strict musical terms, vibrato is a cyclic change of the frequency of the note, while "tremolo" is a cyclic change in the amplitude of the notes. The amp and effects makers have used the terms interchangeably a lot, so for amps and effects, you cannot tell what you will be getting from the term. ========================================================================== Where can I find schematics for guitar effects? Books "Electronic Projects for Musicians" by Craig Anderton "Electronic Projects for Guitar" by Robert Penfold which outline not only the schematics, but how to read them and how to find parts, how to make boards and packages and boxes, etc. If you have no experience with effects, get one of these books first. In fact, get them anyway. They are very good references for people interested in effects. Magazines Other schematics are available commercially in back issues of Guitar Player magazine, where Anderton wrote an irregular series of articles starting in the seventies in which he would outline an effect and how to build it. Some of these are significantly different from or more flexible than commercial effects. Other electronics-related buildit magazines have published articles on the odd effect or two over the years. These include Popular electronics, Radio-Electronics, Electronics Technology International, Electronics Today, a little-circulated rag called Poly phony, and another called Electronotes (although the Electronotes articles are primarily oriented towards analog synthesizers). Kits Effects kits are available from PAIA Electronics, 3200 Teakwood Lane, Edmond OK, 73031, 405-340-6300. It is useful to write these folks and request a catalog if you're interested in effects. John Simonton is the president at PAIA, and is on line at PAIA.aol.com, or was for a while. The Net There are a few schematics available as postscript files at ee.bode.ualberta.ca. There is a WWW page maintained by Jamie Heileman that is now beginning to have a good collection of schematics in postscript form. Jamie has been embellishing this collection at a fair clip. It is likely that this will grow to seventy or eighty schematics over time, although it has only twenty or so now. This can be reached at http://www.wwu.edu/~n9343176 There are some schematics on the Analogue Heaven Web page or its connections at: http://www.cs.washington.edu/homes/map/analog/ Informal Sources The ...ah... less structured... ways to find schematics are to know someone who has them somehow, like a musical instrument repairman, or to trace out the schematic from a commercial unit. There are a number of people who have collected libraries of schematics for effects, if you can find them. These folks usually want to trade schematics to build up the library. [continued in section 2 of 3] Effects FAQ.2 Effects FAQ.2 From [email protected] Sun Dec 18 11:35:55 CST 1994 From: [email protected] (RGKeen) Newsgroups: alt.guitar Subject: Guitar Effects FAQ 2/3 Date: 18 Dec 1994 10:57:05 -0500 Sender: [email protected] Reply-To: [email protected] (RGKeen) [Guitar effects FAQ, section 2 of 3] ========================================================================== How practical is building your own effect? It is NOT cheaper to build your own than to buy, at least in most cases. If you want to tinker and play around with building effects because you like it, go ahead. Also, if you're after a vintage effect, the prices may be so outrageous for re-creations or originals that you can duplicate it for a song. (sorry, I had to...) If you want a few effects and think it is cheaper to build your own, think long and hard about it. The economies of scale being what they are, the commercial companies can produce a finished effect and sell it at retail for less than your cost of parts. Common semiconductors are from three to ten times cheaper in thousand unit lots than in ones and twos. Finished, painted,lettered boxes to put this stuff in are ten to fifty times cheaper for a manufacturer to make than for you to do. See Appendix A - Effects Economics 101 below. Most people who start down this path never build an effect. Effects are hard to build -* mechanically *- not electronically, so the interest in electronics is immediately subverted when you try to package one. Making one reliable under typical music conditions is even harder. If you are not already involved to a signifcant degree in electronic tinkering, it will be expensive to acquire the tools and parts to build effects. Faced with these problems, most folks give up. If, on the other hand, you just love tinkering with guitar effects, have some electronics know how, and have some money to put into the hobby, forge ahead. It is my personal choice of a good time. Has been for a couple of decades. You have to be really good with digital logic and programming as well as prototyping to make a sophisticated Digital Signal Processing kind of integrated effects box like the rack units. With some experience, you can make effects which are not commercially available, or have your own personal likes written into the wires and parts. It is also in general NOT possible to build a good wah pedal or other rocker kind of pedal, as the mechanical construction of a reliable rocker-pedal mechanism is impractically difficult for the average Joe. However, you can often find a dead-or-dying Cry baby or other wah pedal to cannibalize for the case and pedal; I've seen dead ones for as little as $15. Oh, yeah... what about what you thought this section was about. Yes, you can build effects that perform as well as commercial units, or surpass them in terms of noise, performance, etc. It's not hard, for the analog kind of stomp box. ========================================================================== Skills and tools for building effects There are some minimal skills and tools you'll need to be able to understand an effects schematic and have some hope of building something similar. Reading Schematics You'll have to be able to understand what the schematics are telling you. A schematic is a form of shorthand which just tells what parts are hooked together and what the values of the components are. There are many ways to physically wire up the same schematic. Unfortunately, there is no super easy way to understand schematics without some basic understanding of the electronic parts for which the symbols stand. I recommend you pick a book or two from the bibliography and put in some study time if you have no electronics background. Basic Construction Tools For circuit boards: Pencil soldering iron (15-25 Watt) Needle nose pliers Small diagonal cutters Rosin core solder (acid core plumbing solder will eat up your circuit boards) For Boxes: Straight and Phillips screwdrivers Electric drill and bits Hack saw File Nibbling tool Basic Construction Skills You'll have to be able to get the electronics to work to complete an effect. This generally means soldering parts to a circuit board. Although it is possible to solder the parts all together, space-frame style and then pot them up in epoxy or something, or to use wiring lugs, I don't recommend these methods (and I've done both of them!) Skills Bibliography Reading Schematics "The Design and Drafting of Printed Circuits" by Darryl Lindsay, Published by Bishop Graphics ISBN 0-9601748-0-X Electronics Construction: "Electronic Projects for Musicians" by Craig Anderton "Electronic Projects for Guitar" by Robert Penfold Soldering (under construction) ========================================================================== Effects Packaging This is HARD. An effects box needs to be sturdy, and either metal or lined with metal or a conductive paint to keep the circuit from picking up hum or radio interference. It needs to be big enough to hold the circuit, but compact enough to be usable. I have bent up boxes from sheet metal, with varying results, but to be sturdy enough, you need very heavy (hard to cut and bend) sheet metal. Worse yet, good effects boxes are hard to find in commercial lines as well. There are a few bent sheet metal boxes that are about the right size and shape, but might not be durable in heavy use. Open up some commercial effects cases to start getting an idea about what is common in effects. You can package several effects together in a rack enclosure or in some of the schemes espoused by Anderton. I don't personally like this, but it is a reasonable way to package your effects. Penfold doesn't say much about boxes, for some reason. A good box for an effect should be about 3 inches wide, 5 inches long, and 1 1/2 to 2 inches deep. A sloping front for the bypass switch is nice, but not essential. A very good starting point is the line of Hammond die cast aluminum boses - tough, durable , easy to work, almost ideal. Try the 1590B or the 1590BB, about $10 from DigiKey or Mouser. The 1590BB is a cast aluminum box with a fitted base/cover. It is very durable, and inexpensive in quantities of one. It is reasonably easy to find, and about the right size for an effects box. The early MXR effects like the Phase 90 and Distortion plus were packaged in a box the size of the 1590B, just slightly smaller than the 1590BB, and were very tightly packed indeed. The 1590BB is big enough for a non-manufacturer to get a whole effect shoehorned in. Other boxes that are about right are: Hammond 1590B -similar to the 1590BB, but smaller, the size of old MXR's Hammond 1590C -similar to the 1590BB, but bigger, about 2 1/4" high. LMB #138 -folded sheet metal, not too sturdy, but cheap LMB #139 -folded sheet metal, not too sturdy, but cheap LMB MDC 642 -folded sheet metal, sturdier, moderate price LMB MDC 532 -folded sheet metal, sturdier, moderate price LMB UCS 1 3/4-5-5 -folded sheet metal, much sturdier, also pricier Putting it all in the box Figure out in advance where things will go inside the box and how the board will mount, where the controls go, and where the battery mounts. This amounts to a three dimensional layout of the box. Once you are sure of your layout, mark and drill the box for mounting holes for the jacks and controls. Do this before painting or finishing the box. A big part of making it come out right is the right selection of controls and their placement on the box. Think about commercial effects you may have used, and how the controls are placed, how close together they are, etc. Make several drawings, or better yet, mount your controls in a cardboard or foam-board mockup of your effects box before you drill and possibly ruin your box. It is easy to drill holes and hard to grow them closed again. Making It Look Good There are lots of ways to do this. Anderton outlines several in his book. My preference is to paint it with a good primer, bake it in my oven at 200 degrees for an hour, cool, and paint with an auto touch up paint, then bake again. When this is cool, the paint should be reasonably durable. If you use a light color, you can use your laser printer or copier to print labels on clear laser-printer labels from an office supplies store, and letter the controls easily and neatly. If you use a dark color, the direct transfer lettering from electronics shops will work, but this will need another coat of clear spray to be durable. Best of all is to get the box powder coated and baked, then have it screen printed. This is really only affordable if you or a friend already have the equipment and skill to screen print, but it produces a commercial-quality finish. I have seen this done, but never done it myself. ========================================================================== Procuring Parts I used to try to ferret out the used- and surplus-electronics stores in a town to see what I could find cheaply. Two suppliers have changed my habits. These are DigiKey and Mouser. They stock a broad line of electronics parts, including parts to make packaging easy, and although their prices are not the best possible deals or surplus, they are reasonable for first quality commercial goods. They ship fast, and stock what is in their catalogs. Mouser, in particular ships the same day as your order, and sinc e they have a warehouse in Dallas, I get my parts the next day. Both Anderton and Penfold have good discussions of which parts are good, and which are not. I will add to that only where I think I'm really adding. I list some recommended suppliers in the next section. * Integrated circuits Anderton's circuits used some strange op-amps and some opto-isolators that are not easy to find, although they DO exist. Most commercial effects except recent Japanese ones pretty much stick with either single or dual 741-style op amps or CMOS logic IC's which are easy to find. * Transistors and diodes Some of the more interesting effects used germanium transistors and diodes. You can occasionally find germaniums in surplus places and you can find germanium diodes in Radio Shack, of all places. Ordinary silicon diodes are in Mouser and DigiKey. I usually don't buy from Radio Shack except as a last resort, like if you need a connector RIGHT NOW. They are more expensive. * Resistors and Capacitors Mouser and DigiKey. Read their catalogs and select parts BEFORE you do your layout, then the parts you actually get will fit in place on the board. * Jacks, switches, knobs, etc. This is the kind of stuff you usually think of last. Big mistake. The classic stomp box has this big metal switch you stomp on to switch it in and out. This switch is the Carling 317PP. It costs $15 (yes, apiece!) in unit quantities, and only drops to $8 in hundreds. I have not found a good replacement that is the same function. Just the economics of this switch has driven me to adapt some form of electronic switching in my effects, as I can make an Anderton-style CMOS equivalent for less than $3 in parts and one square inch of circuit board. It is really important to know this before you hack up your box. (I understand that Maplin Electronics in the UK has Arrow DPDT stomp switches for the equivalent of $6 US, so this might help if you can buy from them) The control pots are another problem. Effects units in small stomp boxes need small controls to fit in the box. It is usually hard to locate a set of small, physically similar pots in different values for an effect. Manufacturers can do this because they can buy large numbers and get essentially anything they want. A bright spot is Mouser's selection of miniature pots, for about $1 apiece, in many values. ========================================================================== Some recommended suppliers are: In the USA: Mouser Electronics Mouser Electronics Mouser Electronics 11433 Woodside Ave. 2401 Highway 287 North 12 Emery Ave. Santee CA 92071 Mansfield TX 76063 Randolf NJ 07869 Mouser Electronics 370 Tomkins Court Gilroy CA 95020 Catalog Subscriptions: (800) 992-9943 (Continental US only) Sales & Service: (800) 34-MOUSER (800-346-6873) (US, Puerto R., Canada) Very complete catalog of brand-new components. Usually quick service, $20 "minimum" ($5 charge under $20). When ordering, you may want to be sure to ask about availability and shipping locations; they have several warehouses, and frequently orders will get sent from several warehouses (which drives up the shipping costs). Export orders have a $100 minimum, except for Canada and Mexico. Digi-Key 701 Brooks Ave. South P.O.Box 677 Thief River Falls, MN 56701-0677 +1-800-DIGI-KEY (344-4539) +1-218-681-3380 (FAX) No minimum, $5 handling under $25, free and very complete catalog, very nice indeed. Prices aren't always the best, but rarely excessive. Maplin Electronics is a BIG supplier to the home hobbyist of electronic parts and kits in both the UK and Europe. They can be contacted at: Maplin Electronics PO Box 777 Rayleigh Essex SS6 8LU UK Fax: +702-553935 Modem: +702-552941 (sorry, don't know paramaters, try 2400,8bit,1 start,1 stop) Maplin is reported to sell an Arrow DPDT equivalent for 3.76 pounds (~$6 USA) each in one off quantity. (I'll have to try that one!!) Antique Electronic Supply lists the following germanium transistors: Part No Description Price ($US) U-TRB-1 PNP similar to 2N107, 2N218, CK722 etc $1.49 U-TRB-4 NPN similar to 2N170 $1.69 U-TRB-5 NPN similar to 2N193, 2N388, 2N1302 $1.29 U-TRB-6 NPN similar to 2N170, 2N292 $.95 U-TRB-7 PNP similar to 2N111,2N139, 2N218 $.95 U-TRB-8 PNP similar to 2N107, 2N218, CK722 $.95 The address is: Antique Electronic Supply P.O Box 27468 Tempe, AZ 85285-7468 USA Ph (602) 820-5411 Fax (602) 820-4643 Hosfelt Electronics has the CLM6000 opto-isolator that is ubiquitous in the projects in Craig Anderton's book. They are about $3.50 US apiece. Hosfelt Electronics 2700 Sunset Blvd. Steubenville OH 43952 +1-800-524-6464 +1-614-264-5414 (FAX) No minimum, $3.75 S&H. Surplus electronics. The Electronic Goldmine has a good listing of surplus electronics, useful for run-of-the-mill construction. Electronic Goldmine P.O. Box 5408 Scottsdale AZ 85261 1-602-451-7454 voice 1-602-451-9495 fax ========================================================================== Answers to questions about fixing broken effects Q. My Belchfire Megablaster pedal doesn't work at all. How can I fix it? A. Most completely dead pedals - this means that no sound comes out of the pedal at all either when the pedal is not switched to bypass or in either position of the bypass switch - are either wiring or battery power related. Open up the effect, taking care to note how it came apart so you can successfully put it back together. Carefully examine all of the wires inside the box. All wires should be firmly soldered at both ends. If there is a wire with one end loose, carefully examine all of the places that it might have connected to, perhaps with a jeweler's loupe, ($5 at most hardware stores, very handy) to find where the wire broke off as it left the soldered joint. Wires almost never break in the middle of the wire, as there are tiny nicks in the wire where the insulation was stripped away. The wire breaks at the nicks when it is flexed too much. Melt the solder at the joint an push a wooden toothpick into the hole to make room for the wire. Carefully strip a little insulation off the remaining wire and push it into the hole, then solder it. If you find no broken wires, suspect power problems. This will sound a little simplistic, but measure the battery voltage, both with the battery out of the circuit and with it clipped in and the effect working. The battery may be dead, or alternatively may not have enough oomph left to run the effect. The battery voltage should be at least 7 volts when it is actually running the effect. Measure this by poking voltmeter leads on the battery terminal, poking it between the battery and the battery clip (easy for a 9V battery). If the voltage is low, the battery may be dead, try a fresh one. If a new battery does not help, there may be a short on the board. Sometimes the isolation of the circuit board from the case is messed up somehow, and the board shorts out to the case. If this is true, the effect will work when the case is open and the board pulled loose from the case. The short may be a signal short, in which case the battery testing will not find it, or a power short, which will be caught. There may be an open wire between the battery and circuit board. Connect one voltmeter lead to the case ground at the input or output jack, and measure the voltage at the place where the battery lead goes onto the circuit board. Note that for effects which use either the input or output plug to switch power on, you'll have to stick a plug into the approprite jack to connect the battery up. This is very common, so you may just want to plan to stick a plug in each jack. If you don't read battery voltage going onto the board, something is open between the battery and the board. The easiest way to find this is to stick one ohmmeter lead on a battery terminal, poking it between the battery and the battery clip and the other on the ground or + voltage respectively at the circuit board. There should be almost zero ohms from the battery terminal to the board. The path from battery to board may go through a jack (often the (-) terminal does this), or through a power jack for external power (frequently the (+) terminal does this). You can rapidly go down the wiring chain from terminal to terminal until you find where the connection stops; you will have just passed the break. Sometimes the battery clip has a broken wire inside the plastic holder that fits on top of the battery. This is why you should connect directly to the battery terminals. If one of these tricks doesn't catch it, there is probably a fault on the circuit board, and you'll need to be able to debug it from the schematic, or trace out the board to make a schematic to work from. This is much more complicated, and you should only try this if you already know how. If you don't already know how to do this, get someone who does to fix the pedal for you. If the effect is not totally dead, just sounds wrong somehow, it is probably a circuit board problem, and needs the circuit board tinkering to fix it. Q. My (MXR Micro Chorus/EH Electric Mistress/ EH Memory Man/others) delay or chorus pedal doesn't delay/chorus/etc anymore, although sound comes through it in both effect and bypass positions. How can this be fixed? A. This is one of those rare cases where you can have an effect that can't be fixed, at least not easily. A common cause of this malady is that the analog delay chip, a Reticon SAD512 in the Micro Chorus and a Reticon SAD1024 in the others, is not commercially available any more. The only options are cannabalizing another box that contains one, or hacking in one of the Panasonic MN3xxx series delay chips. This hack is almost certainly possible, but I have not seen one fixed this way yet. Q. My wah pedal sounds scratchy/noisy when I move the pedal. Can this be fixed? A. Yes. First step is to look at the pot that is rotated when the pedal is moved. If this pot is an open style pot (there are holes that go through into the innards), get a can of non-residue contact cleaner at an electronics supply store. Squirt some of this into the hole and work the pedal/pot back and forth a lot while it evaporates. This MAY cure it. If the pot is sealed, no holes into the interior, you may have to replace it. The manufacturer may have the actual part with the little gear, saving you a LOT of time and effort. If not, it is possible to get a new, same value pot and cut the shaft to length, drill a little hole for the pin that keeps the gear from slipping on the shaft, and reassembling. This requires some significant mechanical aptitude, though. A slam-dunk solution is to refer to Craig Anderton's article from Guitar Player entitled "Clean up your Volume Pedal" , only use the LED/LDR pair to replace the pot on the Wah. I have done this for a friend who wanted to have a remote pedal, the actual Wah circuit back in his rack. Worked Great. ========================================================================== Appendix A - Effects Economics 101 An effect that you build will likely cost you box $10 jacks 2 stomp switch 15 (for Carling; 3 for electronic) paint 4 controls 2 knobs 1 wire 2 PC board 3 electronics 5 - 12 for a total of $32 to $51 if you have to buy all this stuff new. This does not count any tools or other supplies like solder, pliers, etchant, and so forth, nor does it count your time and effort. Musician's Friend sells stomp boxes for $30 to $100, the top end being some things that are not really reproducable at home. Notice that the electronics that do the work are only 1/3 to 1/10 of the cost of the finished article. ========================================================================== Appendix B - Making Circuit Boards A lot depends here on whether you are building something from a schematic that has no provided layout or you are using a magazine article that has an already laid out circuit pattern to follow. If you are doing the latter, you don't need to worry about how to make up your own layout. If you will be working from a schematic only, you will probably need to lay out your own board for the effect. You really ought to make a semi-formal layout or some sketches even if you intend to make only a perfboard or stripboard version. There is a much more complete FAQ on making printed circuit boards over on sci.electronics. I have thrown in only some basics. Layout > Laying out the board. Go to your local used book store and in the technical books section, find a book with a title something like "Printed Circuit Drafting and Layout". Read it, ignoring the things about how to lay pads and tape on mylar film, but paying attention to the sections on how to orient parts and run traces to and between them. You can, of course skip this if your effect is a copy of a magazine article which contains a printed circuit layout. Lay out your board, keeping the board type you will make in mind. There are some tools which will make this easier. For general layout, get grid-ruled paper and tracing paper to draw sketches of layouts on, and a couple of colors of pencil, red and blue being traditional. In general, make your board from a set of postage-stamp circuit fragments, each of which is a tightly connected lump of stuff, usually about one IC and its immediately connected resistors and stuff. Most circuits are a set of such clumps, with signal and power supply lines going between them. make the fragements, then interconnect them. Make all the wires come off one side of the board, not all around it where you will have to knit the board into the box, and certainly not coming out of the middle of the board. Have the inputs on one side of the board, and let the signal progress through the board like on the schematic, in one direction to avoid having unwanted feedback paths. Do not forget to leave some way to mount the board in the box. Wrapping the whole board in plastic foam and leaving it loose in the box is evidence of such forgetfulness, although that is exactly what MXR did in all its early production. Perfboard > Perf board and Strip board methods. Hack a chunk of circuit board big enough to implement your layout. Read Penfold for the full description of the stripboard method. For the perfboard method with pad-per-hole board, bend the component leads to insert them into the board, then use the excess lead length below the board to make "circuit traces" by bending them flush with the board and routing them from connection to connection. Use wire wrap wire to connect things that the leads can't easily. Solder the leads where they go through the board, and at connections. Solder as you go along, placing a few parts and soldering them. This method is remarkably easy to do, and is reasonably durable if your soldering technique is good. It is about as fast as doing a board layout, so if you have some experience, you can lay out the circuit from the schematic as you go. I would, however, never, ever make more than one of a kind this way. If I think I might EVER make another I would lay out a printed circuit board. [continued in section 3 of 3] Effects FAQ.3 Effects FAQ.3 Fix Reverb Ground Hum Fix Reverb Ground Hum http://www.webervst.com/wwwboard/amps/messages/11903.html any easy fix? you bet...and here's the answer... --------------------------------------------------------[ Follow Ups ] [ Post Followup ] [ Amps ] --------------------------------------------------------Posted by mark n on April 25, 2000 at 08:16:40: In Reply to: Re: DIY 6G15 reverb hum - any easy fix? posted by David Allen on April 25, 2000 at 06:49:46: : : Try replacing the 100-ohm heater resistors with a 250K pot, and play around. Likely you have a conflict with the heater circuit ground. : : I had this problem with my Marshall 18W clone, damned near drove me nuts. Turned out that it wanted one side of the heaters grounded, and the other isolated by a 220K. Weird. : Did you use a shorting type input jack? Make sure it is good or it will hum. I like to establish an AC ground at one of the PT mounting bolts for the HV center tap, AC power cord ground, heater grounding resistors and so on. The DC star ground is for all the other signal grounds including the ground side of the filter caps. Make sure the 6K6 is connected to the choke properly or it will hum. I'd try to figure it out because this circuit is bad about humming when you have an amp involved. Plug both the amp and the reverb unit into the same grounded outlet. : Good luck. David ---------> you, sir, have a ground loop. if this is a nasty, intense buzz, then chances are the problem is not *in* the reverb unit, but is associated with the interaction of your amp. you properly note that the original units were not grounded, and you speculate that lifting the green wire will fix the hum. it will, but don't do it. for safety reasons, keep all audio equipment "3 prong".....hard grounded chassis. the solution is to make a special inter-connection cable. make a 1/4" - 1/4" "guitar cord", however, be careful to only connect the shield on one end. if this were to be used on a guitar, it wouldn't work. but since both pieces of audio gear are grounded [i.e. frames connected] then the shield need not be joined at both ends. use this cable to connect your reverb's output to the amp's input. conventional wisdom says to plug the 1/4' plug with the ground connected to the amp; use the ungrounded plug for the reverb side. this should 100% cure your loop. a word to the wise...especially if you gig out: you now need a special cable...make 3 or 4 of them, just incase you suffer a "stage failure". furthermore, when i make special 'lifted' cables like this, i ALWAYS use bright shring wrap on the non-grounded end for identification purposes. good luck!! ------------>mn --------------------------------------------------------- Follow Ups: --------------------------------------------------------Post a Followup Name: E-Mail: Subject: Comments: Optional Link URL: Link Title: Optional Image URL: --------------------------------------------------------[ Follow Ups ] [ Post Followup ] [ Amps ] Flea Market Checkout Flea Market Checkout From [email protected] Sat Oct 25 22:17:44 CDT 1997 From: [email protected] (Mark Garvin) Newsgroups: rec.music.makers.guitar,alt.guitar Subject: How to check amps at flea markets and pawn-shops Date: 25 Oct 1997 17:25:59 -0400 Xref: geraldo.cc.utexas.edu rec.music.makers.guitar:164644 alt.guitar:204618 (Prev thread was "Fender Vibro Champ"): > Puma writes: >I saw a used one of these in a pawn shop. They were >asking 175.00. It is missing one of the tubes. >Is this a good amp? Is this a good price? A couple things occurred to me while reading the post above. It's not always possible to listen to a flea market or pawn shop amp, so there are some things you should be aware of: The most important thing in an old amp is the transformers. If they are toasted, you're in trouble. Speakers are next, but those can be replaced more easily. The very least you should do when buying an amp is to (first) check the fuse to make sure it's the right value, and then make sure that the tubes light up, etc. Sometimes not possible to plug a guitar in, but listen for normal background hiss. This is some indication (but NOT a guarantee) that the transformers are OK. NOTE!: Very old amps that have not been powered up for a while may have bad electrolytic (filter) caps. In that case, I recommend NOT powering the amp up. Having a good repair shop do the testing. Do not pound power chords thru an amp that is not making any sound!!! Three !!!'s warranted. This often means that the speaker has been blown or disconnected. On some Marshall amps, the impedance selector comes loose. Players who crank the amp and play loud to see if they can get any sound will often fry the output tubes, the output transformer, or even tube sockets (Really!). This happens due to high voltage spikes that can occur when no load is connected (flyback effect like high voltage generators in TV sets). Arcs occur and carbonize anything in the path (hence socket replacement, etc). This seems like common sense, but I've had amps come to my shop that were supposedly checked by pro service men--they've had 30 amp fuses, aluminum foil, pieces of wire, etc. in the fuse holder. This sometimes means that the owner couldn't find the right fuse and the service shop didn't check. Other times it means that the amp kept blowing fuses of the correct value, and the owner 'corrected' the problem with a short circuit. Ex: I saw an old BF bassman that had developed a short in one of the output tubes. When it started blowing fuses, the owner put in a 20 amp fuse. So instead of blowing the fuse, the amp melted down the filament windings on the power transformer. A bit more expensive than a fuse. (The inside of that Bassman also looked like a giant roach motel! They had Barco Loungers and a shuffle-board court set up in there!...But that is a revolting subject.) The original post mentioned that one of the amp's tubes was missing: Some tube amps (like the Champ) have tube rectifiers. Service shops occasionally install internal solid state rectifiers and pull out the rectifier tube. When this is done, the socket should at least be taped over, and marked with a warning not to install the tube rect. Watch for this. Fender tube charts show which is the rectifier socket. It's usually a tube that starts with a '5' (like 5AR4 or 5U4), but not always (not in the Champ). The down side of the solid state rectifier substitution is that s.s.rects do not drop as much voltage as tube rectifiers. Wall socket AC voltages have been getting higher over the years (often 127 vac in NYC), so old amps' power supplies will usually run high to begin with. Most modern output tubes are not as tolerant of high voltages as the older American or European brands, so many flame out from over-voltages-esp 6V6's (Champs, Deluxe Reverbs). Swapping in solid state rects compounds the situation cause they drop less voltage. That mod can usually be reversed easily by a competent repair shop. Amps that still run high can sometimes be helped a bit by using a different rectifier tube (see old alt.guitar.amps articles for info). I recommended listening to make sure the amp was at least making normal background noise (hiss). Well, that's not always possible at flea markets that have no AC. Keep in mind that those amps may be toasted, so the value will be hard to determine. If the amp makes *some* sound, at least there is a chance that the transformers and speaker are good. Those are the most expensive components. Old transformers are often impossible to find, so replacements can require cutting larger holes in the chassis and other ugly mods. Very old amps have two-conductor AC cords. I have some reverence for vintage amps, but unless the amp is for display only, I never flinch at replacing those with new 3-wire grounding plugs. Have a competent tech do this. Better consider the shock hazard if the amp is not properly grounded. In fact, make sure that ALL your gear is grounded correctly--it only takes one badly wired device! Yes, guitarists have gone out in a blaze of glory because of wiring problems (supposedly incl Keith Relf from the Yardbirds). One last trivial thing, since the original thread was about Champs... Many have blown speakers. Tube Champs used 4 ohm speakers and had no screen resistors. The technical reason for this is beyond current scope, but I recommend finding 4 ohm replacement speakers. Using 8-ohm speakers in a Champ cranked to 10 will often fry the output tubes. I've also posted about this in old alt.guitar.amps articles, so I won't elaborate here. I hope that helps to make buying decisions a bit easier. The little old lady who only overdrove her Tweed Bassman at church on Sunday is a myth, but I've found some nice old Fenders, Ampegs, etc at flea markets-even in NYC! It helps to look for a couple of those things to make sure repairs won't exceed the value of the amp. MGarvin Mr. Moron improves his signal to noise ratio by 12.6% From [email protected] Sat Oct 25 22:17:51 CDT 1997 From: jesmiley Newsgroups: rec.music.makers.guitar,alt.guitar Subject: Re: How to check amps at flea markets and pawn-shops Date: Sat, 25 Oct 1997 18:05:13 -0400 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Xref: geraldo.cc.utexas.edu rec.music.makers.guitar:164687 alt.guitar:204661 Mark Garvin wrote: > (Prev thread was "Fender Vibro Champ"): > > > Puma writes: > >I saw a used one of these in a pawn shop. They were > >asking 175.00. It is missing one of the tubes. > >Is this a good amp? Is this a good price? > > A couple things occurred to me while reading the post above. It's not > always possible to listen to a flea market or pawn shop amp, so there > are some things you should be aware of: > > The most important thing in an old amp is the transformers. If they > are toasted, you're in trouble. Speakers are next, but those can be > replaced more easily. > > 8< snip a lot of good advise >8 > > MGarvin > > Mr. Moron improves his signal to noise ratio by 12.6% I would also advise smelling the thing. Burnt electronics has a distinctive odor. So give it a sniff, look at the fuse, turn it on, give it another sniff and listen. J. remove the PA to reply From [email protected] Sat Oct 25 22:18:12 CDT 1997 From: [email protected] (Mark Garvin) Newsgroups: rec.music.makers.guitar,alt.guitar Subject: Re: How to check amps at flea markets and pawn-shops Date: 25 Oct 1997 20:23:39 -0400 Xref: geraldo.cc.utexas.edu rec.music.makers.guitar:164676 alt.guitar:204649 >Mark Garvin wrote: >> ...not always possible to listen to a flea market or pawn shop amp, so there >> are some things you should be aware of: >> >> The most important thing in an old amp is the transformers. If they >> are toasted, you're in trouble. Speakers are next, but those can be >> replaced more easily. > jesmiley writes: > I would also advise smelling the thing. Burnt electronics has a distinctive > odor. So give it a sniff, look at the fuse, turn it on, give it another sniff > and listen. Good addition, J. I've also run into a lot of old Fenders with toasted screen resistors. Less pungent odor than (more serious) burnt transformers. MGarvin Please excuse possible multiple post. Server problems I think. Hammond Organ Buys Hammond Organ Buys From [email protected] Tue Jun 8 12:47:41 CDT 1999 From: [email protected](Lord Valve) Newsgroups: alt.guitar.amps Subject: Re: other "tonewheel" organs..... Date: 8 Jun 1999 07:10:18 GMT X-NETCOM-Date: Tue Jun 08 2:10:18 AM CDT 1999 Xref: geraldo.cc.utexas.edu alt.guitar.amps:183591 In <[email protected]> [email protected] (MCAS NV) writes: > >Are there any other Hammond tonewheel organs other than the B3 which might be >bought for less money and still deliver that great sound.....? > >Sorry if this is slightly off-topic. Lord Valve Speaketh: Well, them gee-tah pickahs can kiss me fat BUTT if'n they don't like talkin' about Hammonds...besides, the dudes on alt.music.hammond-organ are some of the most uptight wankers you'll ever want to see. Worse than RAT! What better place than AGA, hmmmm? Anyway, the good ones are the C-3, which is a set of B-3 guts wrapped in different furniture (slab-sided, instead of legs, with a back on it that goes all the way to the floor; this was so lady organists could play in church without folks looking up their skirts) and the A-100, which is a set of B-3 guts mounted in a console along with a couple of power amps, a set of reverb springs, and three speakers. (Usually, all Jensen Alnicos.) On the spinet side of things, you have the M-3, which is basically a B-3 with the bottom two octaves lopped off, and only one octave of pedals (actually, only 12 pedals, from C to B) instead of two. M-3s sound really good for rock music, since the rest of the band is so goddamn fucking loud that you can't hear the bottom two octaves of a B-3 anyway. (Sorry, had a Jazz Snob attack. I'll try to behave... :) M-3s can be had for a song...you can pick 'em up for $250, $100, even $50 sometimes. A good way to catch your first case of Hammond fever; if it gets worse you'll need a B-3, C-3, or A-100 for sure. However, many guitarists are completely overwhelmed at the prospect of having more than six notes available at one time, and retreat to the relative safety of strings and picks. Oddly enough, many of the really good Hammond players I've known over the years started out as drummers; good hand-foot independence is a must if you're going to kick bass pedals, and drummers are trained in this from the git-go. So... there are a few other Hammonds which B-3 afficionados will settle for, and I've listed most of them. If you want the best bang for the buck, shoot for an A-100...you occasionally see these for $500 or less, and they've usually spent their days as a piece of furniture in some rich lady's house. If you rip out the speakers, the amps, and the reverb unit, what's left is a B-3, and it's the *best* gigging organ there is, because a gutted A-100 is 3-1/2" narrower and 80 pounds lighter than a B-3. Lord Valve CHAT WITH LORD VALVE: Log onto any DALnet server and go to channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NOW ACCEPTING VISA, MASTERCARD, AND DISCOVER! "I got the chop...I'll never get popped." - Tower of Power Hammond Tonewheel Organs Hammond Tonewheel Organs From [email protected] Sun Jun 6 12:02:53 CDT 1999 From: [email protected](Lord Valve) Newsgroups: alt.guitar.amps Subject: Re: LV...What's a Hammond B4 worth... Date: 6 Jun 1999 08:18:02 GMT X-NETCOM-Date: Sun Jun 06 3:18:01 AM CDT 1999 Xref: geraldo.cc.utexas.edu alt.guitar.amps:183206 In <[email protected]> Simply Steve writes: > > > >Lord Valve wrote: > >> Lord Valve Speaketh: >> Hmmm..B4 doesn't mean anything to me, but I believe an S6 is a >> Hammond Extravoice chord organ. Did it have a single keyboard, >> with a bunch of accordian-type buttons to the left of it? If >> so, it's an interesting piece, but not worth much. It isn't a >> tone-wheel organ, it uses tube-type oscillators. Accordian >> players love 'em, though..they can kick ass on 'em. > >Curiosity about this tone-wheel technology... >Exactly how does it work? > >SS > Lord Valve Speaketh: A Hammond tone-wheel organ uses actual (miniature) mechanical alternating current generators to produce the frequencies used by the organ. These consist of a pickup (exactly the same, in principal, as a guitar pickup) and a "tone wheel," which looks more like a gear than anything else. All the tonewheels are driven by planetary gears from a central shaft, which is powered by a hysteresis-synchronous motor. (BTW, Laurens Hammond invented the synchronous motor, which made it possible to have *accurate* electric clocks. The earliest Hammond organs say "Hammond Clock Company" on 'em! Ol' Laurens invented the spring reverb, too, and a whole shitload of other stuff.) Since all the tonewheels are driven from the same shaft, the organ *always* stays in relative tune...a Hammond *cannot* go out of tune, or be tuned. The synchronous motor will turn at the correct speed as long as it receives 60 Hz, and the organ will be in tune. The frequency of the "A" produced by a Hammond is specified on the original patent sheets as 440.000, which ain't too shabby for a device invented in 1934. I calibrate my strobe tuner with my B3, in fact. Anyway, each metal tonewheel has "teeth" (or bumps) around the edge, and as the wheels spin, the teeth interrupt the magnetic field produced by the permanent magnets in the pickups; each pickup has a coil of wire around a cylindrical magnet with a blunt conical point, and as each tooth on the tonewheel passes the tip of the magnet, one cycle of alternating current is induced in the coil. If 440 teeth pass the magnet tip every second, you have an "A." There is a toneheel and a pickup for every frequency generated inside the organ; for a B3, I seem to remember there are 92. The output of each pickup goes through a dedicated filter which removes spurious harmonics, and then all the tones are mixed together by the organist, using the "drawbars." A B3 is really an additive synthesizer, which allows the player to combine a variety of pure sine waves to build any tone he seeks. The drawbars are arranged in the standard harmonic overtone series, ie., fundamental, octave, twelfth, fifteenth, seventeenth, nineteenth, and tewnty-second. (The flat twenty-first was omitted on the B3, but showed up in some of the later Hammonds which don't sound as good.) In addition, a sub-fundamental and sub-fifth were added for body, and it is these two "undertones" which give the B3 more balls than a Tyrannosaurus Rex. "Modern" electronic organs either use samples, or a "top octave generator," which is a chip that produces all of the notes from C to B at a very high frequency; all the rest of the frequencies the organ needs are divided from the top octave. Almost all of the other organs use "subtractive" synthesis, where you start with a harmonically rich tone (a square or triangle or other complex waveshape) and remove harmonics with various filters. Only the Hammond tone-wheel organ builds its sounds from combinations of pure sinewaves, and puts the level of each harmonic under realtime control by the organist. The Hammond "percussion" effect you may have heard organists talk about is produced by keying in a tone which decays (like a struck xylophone) over the top of the continuous tones from the drawbars; if you have trouble imagining what this sounds like, take a listen to "Green Eyed Lady" by Sugarloaf...this is a good example of percussion "crunch" (in the pop/rock idiom, anyway.) Lord Valve CHAT WITH LORD VALVE: Log onto any DALnet server and go to channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NOW ACCEPTING VISA, MASTERCARD, AND DISCOVER! "It ain't braggin', if ya can do it." - Babe Ruth How Long Do Tubes Last How Long Do Tubes Last From [email protected] Fri Jan 10 21:24:34 CST 1997 From: Bart Youngblood Newsgroups: rec.music.makers.guitar Subject: Re: How long do tubes last? Date: Fri, 10 Jan 1997 22:22:18 -0500 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Greg Jones wrote: > > I bought my first tube amp about 4 months ago. What is the average > length of time that I can go before I will have to replace my tubes? > > Will the amount of time that I play and effect tube life expectancy? How > about volume levels and the amount of distortion used? > > How much are tubes? Are they easy to change? What about rebiasing? > > Greg The amount of time you use them will have a definite effect on them. What kind of amp do you have? Some amps that have tons of gain just eat tubes. If you drive them hard all the time, they certainlly will last less. I've head reccomendations that you change them yearly, but I say replace them when you feel they need to be changed. Typically, preamp tubes will outlast power amp tubes, because typically, power amp tubes operate at higher voltages and amperages. Tubes are easy to change, but depending on where you live, may be difficult to obtain. You might have to resort to mail order, and in some cases, you can get them cheaper this way. Tubes range in price from anywhere from about $2 to $200 each. Because of the recent interst in tube amps, tube prices have fell slighlty, as you can get pretty decent power tubes for under $10 each. Rebiasing is essential if you change tube types or manufactuers, or if the amp starts acting up after changing tubes. It's good to have it rebiased anyway about every 2 years (or less, depeneding on usage) becuase the componets gradually lose their tolerances. Bart How Many Watts How Many Watts From [email protected] Sat Feb 11 18:32:35 CST 1995 From: [email protected] (Tremolux) Newsgroups: alt.guitar Subject: Re: 40 Watts...enough for small clubs?? Date: 11 Feb 1995 19:18:44 -0500 Sender: [email protected] Reply-To: [email protected] (Tremolux) First off, a Blues Deluxe, despite Fender's rating, will not put out 40 clean watts. It will put out 40 watts, but at a very high level of distortion. Those amps put out about 30 clean watts. Will it be loud enough for a small club?? Probably, unless you want a real clean tone, in which case you should have gotten the DeVille, which is about 40 clean watts. I commonly use 40 to 50 watt amps at small clubs, and they're plenty. Even my Deluxe Reverb that I've measured at 25 clean watts, is loud enough for a SMALL club. Regards. Magnetics for Morons Magnetics for Morons From [email protected] Tue Dec 1 13:31:08 CST 1998 From: [email protected] (Henry Pasternack) Newsgroups: rec.audio.tubes Subject: Magnetics for morons. Date: Fri, 27 Nov 1998 17:07:24 -0500 Xref: geraldo.cc.utexas.edu rec.audio.tubes:97662 Electromagnetics for Morons. Copyright (c) 1998, by Henry A. Pasternack This article is a review of the basic principles of electromagnetics. It covers some of the basic terminology encountered in discussion of transformer theory. I've tried to be intuitive and avoid the use of any mathematics. Still, it would be good to read this article along with a standard electromagnetics text or especially the RDH. Some of the ideas are challenging and are better understood with the aid of graphs and math. I may find the inspiration to write subsequent articles discussing important concepts missing here, namely electromagetic induction and the operation of chokes and transformers. Introduction. Electromagnetics is the branch of Physics having to do with the properties and relationships of electric currents and magnetic fields. A magnetic field is a "phenomenon" that arises whenever electricity is on the move. Of course, moving electricity implies the flow of electrons in a wire, but it need not be so. For instance a permanent magnet gets its field from tiny atomic current loops formed by electrons whizzing about in their orbits. A magnetic field is hard to describe because it cannot normally be seen, felt, or sensed directly in any way. The field is only tangible through the force it exerts on real-world objects. It can be mapped by probing the field with a tiny magnet. The field will exert a twisting force on the magnet, the strength and orientation of which vary with position in the field. Field lines. Probing with a test magnet lets us draw a three-dimensional plot of the field. This consists of a set of smoothly-flowing field lines. The field lines always form continuous loops. Where the field is intense the lines are bunched tightly together and where the field is weak they are more widely separated. The magnetic field is directional. The direction of the force exerted on the test probe depends on the orientation of the field lines at the point of interest. Field lines cannot be broken. If a field line were to break, the ends would have to terminate on positive and negative particles called magnetic monopoles. Physicists have searched for years for proof that magnetic monopoles exist. As far as I know, they haven't found any, or if they have, magnetic monopoles are so hard to produce and so short-lived as to be of no practical consequence. Magnetic flux. A magnetic field line is called a line of flux. The symbol for flux is the Greek letter "phi" (a circle with a slash through it), and the unit of flux is the Maxwell. One Maxwell corresponds to one line of flux. The flux line is an abstraction; the field is continuous and doesn't actually form into spaghetti-like strands. The flux line is useful because it quantifies "units" of magnetism. Drawing a loop in the vicinity of a magnetic field encloses lines of flux. A flux line is enclosed when it enters one face of the loop and exits the other. For a loop of given area the total enclosed flux depends on the shape of the loop and its orientation relative to the field. The most flux is enclosed when the plane of the loop is perpendicular to the orientation of the field. Magnetic flux density. Dividing the number of flux lines enclosed by a loop by the loop area gives the flux density, that is, the flux per unit area. The symbol for flux density is "B" and the unit of flux density is the Gauss. One Gauss is equal to one Maxwell (one line of flux) per square centimeter. Flux density is a point quanity which means the the loop used to compute it is supposed to be vanishingly small. This means we technically need 3D vector calculus to solve the problem, but we can often get away with algebra in simple cases. Whereas flux is a measure of a quantity of magnetism, flux density relates to the strength of the magnetic field at a particular point. Both concepts are important and it's helpful (and necessary) to learn and understand each of them. Steady electromagnetic fields. The steady flow of current creates a fixed magnetic field in the space surrounding a wire. If the wire is straight, the field lines form concentric rings about wire. Near the wire the field lines are more tightly bundled and the flux density is higher. The field reaches its maximum density at the surface of the wire and diminishes to zero at its center. Forming the wire into a loop consolidates magnetic field lines and increases the density of the flux through the center of the loop. Winding many loops to form a coil increases the flux density further still. The more compact the coil, the denser the field for a given current flow. Magnetic circuits. The path of a flux line, which necessarily forms an unbroken loop, describes a magnetic circuit that is analgous to an electric circuit. The magnetic analogy to Ohm's law relates magnetomotive force to flux and reluctance. Here are the correspondences: Electric Circuit Magnetic Circuit ---------------- ---------------Voltage (EMF) Magnetomotive Force Current Flux Resistance Reluctance The electric circuit model says that the current that flows in a circuit depends on the applied voltage and the total resistance in the loop. Similarly, the magnetic circuit model says that the flux developed in a magnetic circuit depends on the applied magnetomotive force and the reluctance of the loop. The greater the magnetomotive force or the lower the reluctance, the greater the flux developed. Magnetomotive force and reluctance. The symbol for magnetomotive force is "F" and it is measured in Gilberts. "F" developed by a coil is proportional to the number of turns of the coil and the magnitude of the current flowing through it. One Ampere flowing through one turn is equivalent to 1.257 Gilberts. Sometimes the term Ampere-turns is used. Ampere-turns and Gilberts are equivalent except for the scale factor. Magnetomotive force is a measure of the "drive" in a magnetic circuit. Reluctance, "R", is analous to electrical resistance. It indicates the opposition of the core to deve. The higher the reluctance, the lower the flux developed for a given number of Ampere-turns. Reluctance depends on the total contribution of all the materials in the magnetic circuit. Volume-for-volume, air has more much more reluctance than transformer steel. Putting a steel core through a coil results in a much stronger magnetic field for a given current flow. Similarly, cutting an air gap in a core increases the reluctance of the magnetic circuit and reduces the generated flux. To figure out the reluctance of a core, you must know the geometry of the magnetic path and the magnetic properties of all the substances (i.e., steel and air) in the path. That means specifically knowing the value of a quantity called permeability which I will discuss in just a few moments. Magnetic field intensity (magnetizing force). Given a coil producing a constant magnetomotive force (i.e., for a fixed number of Ampere-turns), the shorter the length of the magnetic circuit, the more intense will be the magnetic field. Magnetic field intensity is defined as magnetomotive force divided by path length. It is also known as magnetizing force. The symbol for magnetizing force is "H" and its unit is the Oersted. One Oersted is equivalent to one Gilbert per centimeter. It makes sense that if you have a coil with some number of turns, spreading the coil out (making it longer) will decrease the intensity of the field produced, while squeezing the turns more closely will increase the intensity. This assumes the coil is in air so that the field lines are free to follow the shortest possible loops. If the coil is wound on a core if fixed size, the magnetizing force doesn't change much with coil geometry because the length of the magnetic circuit doesn't change. Magnetic field intensity is closely related to flux density, as we will see in the next section. Permeability. Permeability is analgous to electrical conductivity. It is a property of a material and does not depend on sample shape or size like reluctance. The symbol for permeability is the Greek letter "mu" (or "u" for the font-impaired). Technically the units of permeability are Gauss per Oersted (flux density per magnetizing force), but "u" is usually given as a pure number, the ratio of the permeability of a material to that of air. The permeability of air is defined as unity, so whichever interpretation you choose, it doesn't change the numbers when doing math. Permeability isn't a constant, but varies with flux density. At low flux densities, the permeability is relatively low, but it increases to some maximum value as the flux density increases, and then drops again. For silicon steel, used in making transformers, the initial permeability is about 450 and the maximum permeability is about 8000. Since permeability relates flux density to magnetizing force, if we know how much magnetizing force a coil produces, and we know the permeability of the core, we can compute the resulting core flux density. Plotting flux density versus magnetizing force gives us the all-important B-H curve which is in a sense the "transfer function" of a transformer. It also paves the way for hours of silly speculation and arguments among devotees of single-ended and push-pull amplifiers. Air gaps and distortion. Air is a neutral magnetic material. The permeability of air is low and it doesn't change with applied magnetic fields. Putting some air in a transformer core increases the reluctance and lowers the flux density generated for a given magnetizing force. But it also makes the effective permeability of the core much less sesitive to changes in field strength, and it reduces the tendency of the core to saturate (exceed the point where increases in magnetizing force cause the permeability to the core to decline). This helps linearize the core, reducing distortion. Putting it all together. All this terminology is getting really confusing, so let's go back and run through it one more time. If you have a magnetic core made of some material, you can calculate the reluctance, "R", if you know the permeability, the core cross-section, and the length of the magnetic path. Let's assume for now the core has a simple shape, like a solid steel donut, with no airgap. Now, wind some turns on the core and apply a current. The number of turns times the current gives us the magnetomotive force, "F", give or take a constant multiplier. Divide the magnetomotive force by the average circumference of the core and we get the magnetizing force, "H" (that's Oersteds per centimeter). Multiply "H" by "u" (the permeability) and we get the flux density, "B" (Gauss). Multiply "B" by the core cross-sectional area and you get flux, "phi" (Maxwells). Alternatively, divide "F" by "R" and you're back to "phi" again. The magnetic circuit concept is a short-cut that saves a lot of monkeying around with "B" and "H" and "u". Now, put an air gap in the core. Air has much lower permeability than steel, and much higher reluctance per unit volume. A tiny bit of air suffices to raise the total reluctance of the core. This reduces "H" for a given coil current, and therefore "B" in the steel part of the core. This helps keep the core froms saturating when we run DC in the coil. Our coil produces some amount of flux in the core. Since flux lines form continuous loops, the number of lines in the steel part of the core must be the same as the number crossing the airgap. Since the permeability of air is lower than that of steel, the flux density in the airgap must be lower than it is in the rest of the core. This means the lines of flux must spread out or "fringe" when they enter the gap. Why? Because lower flux density (flux per unit area) means the flux lines aren't so close together. When the flux lines cross back into the steel part of the core, they squeeze back down to their original density. High-permeability materials act like flux vacuum cleaners, "sucking up" and channeling lines of magnetic flux. This is the principle behind mu-metal, a high-permeability material used for magnetic shielding. From [email protected] Tue Dec 1 13:32:51 CST 1998 From: [email protected] (Henry A. Pasternack) Newsgroups: rec.audio.tubes Subject: Magnetics for Morons, Part 2. Date: 1 Dec 1998 19:21:37 GMT Xref: geraldo.cc.utexas.edu rec.audio.tubes:98158 Electromagnetics for Morons, Part 2. Copyright (c) 1998, by Henry A. Pasternack In the first part of this article, I introduced the fundamental terminology of electromagnetics -- flux, flux density, magnetomotive force, magnetizing force, permeability, and reluctance. I explained in a nutshell how these quantities relate to one another. And I mentioned but did not elaborate on the concept of transformer core linearity and the B-H curve. These concepts are enough to explain how the flow of electric current in the primary windings establishes a magnetic field in the core of a transformer. Now I'd like to talk about how we get electricity back out of a magnetic field. This will eventually lead to the subject of electromagnetic induction. I will then be in a position to introduce and explain inductance and inductive reactance, and the operation of chokes and transformers. Moving electrons in magnetic fields. An electron placed in an electric field experiences a force in the positive direction of the field. An electron placed in a magnetic field, on the other hand, experiences no force as long as it remains at rest. Only if the electron is set in motion will the field exert a force on it. The magnitude of the force depends on the speed of the electron, the flux density, and the angle of motion relative to the orientation of the field. Imagine two vectors (arrows of specified length) with their tails anchored to the moving electron. One vector points in the direction of the field and the other along the line of motion. The two vectors define a plane. That is to say, there is exactly one flat plane in space in which both of these vactors lie flat. The direction of the force on the electron is always perpendicular to this plane. The magnitude of the force is greatest when the vectors are at ninety degrees to one another and diminishes as the angle between the two vectors closes. If the directions of the field and path of motion coincide, the plane is undefined and the electromagnetic force is zero. An electron moving directly along a flux line is not influenced by the field. A familiar phenomenon that also obeys this rule is the force exerted by a spinning gyroscope. Undisturbed, the gyroscope sits perfectly still. Try to rotate it and the gyroscope twists at ninety degrees both to the spin axis and the axis of the applied torque. The magnitude of the reaction depends on the angle between the two axes. It's zero if you rotate the gyro along its spin axis. Mathematically, we say the reaction is the cross-product of two vectors. The term "cross-product" comes from vector algebra. By definition the cross-product is three-dimensional. This means we have to think in three-dimensions if we want to study electromagnetism. Permnent magnets and compass needles. Now we can understand why a small permanent magnet twists to align itself with an external magnetic field. A good example of this is a magnetic compass needle. The needle gets its magnetism >from electrons orbiting inside the material it's made from. The earth's magnetic field exerts a force on these moving electrons. The force is transferred to the body of the needle causing it to rotate on its pivot. When the needle is aligned with the field the net torque is zero and the rotation stops. Electron circling in a steady magnetic field. Imagine we have a uniform, constant magnetic field coming up vertically out of a horizontal work surface. Suppose we roll the electron through the field like a marble on a desktop. The electron will experience a steady force in the horizontal plane perpendicular to the direction of motion. The force will deflect the electron into a circular path. The radius of the circle will depend on the charge of the electron and its mass (both physical constants), the strength of the field, and the speed of motion. The deflecting force is always perpendicular to the velocity vector. This means that the field does no work on the electron. Provided there is no friction, no energy is lost or gained and the electron circles indefinitely, neither gaining nor losing speed. Electron in a moving wire. Now imagine a wire lying flat on the desktop. Our electron is trapped in the wire, like a marble in a straw. Draw the wire broadside from back to front through the field. Once again the electron experiences a force perpendicular to the direction of motion. It would like to go into a circular orbit as before but it hasn't enough energy to escape the surface of the wire. Instead, as it is swept through the field the electron is pushed lengthwise along the wire by the electromagnetic force. The electron doesn't accelerate indefinitely. Two things tend to slow it down. First, if the wire has some resistance the force of friction opposes the force due to the magnetic field. Second, the moving electron creates its own magnetic field that cancels the external field. The net result is that the electron rapidly reaches a constant linear velocity in the wire. Viewed from above the electron follows a diagonal path relative to the desktop. The back-to-front component of velocity equals the speed of the wire, and the left-to-right component equals the speed of drift along the length of the wire. The force exerted on the electron by the field is always at right angles to the motion of the electron. Since the electron moves both forward and to the side, it experiences a force to the side and to the back. The sideways force is balanced by friction within the wire. The backwards force is transfered to the wire as the electron bangs into and presses against the wire's inner surface. This force is felt as mechanical drag on the wire as it is drawn through the field. Induced voltage. There are actually many electrons in the wire. All of them begin to drift sideways as the wire cuts through the magnetic field lines. There is no external circuit connected to the wire. The electrons, unable to jump into free space, pile up when they arrive at the free end. The separation of charge sets up an electric potential gradient across the wire's length. A voltmeter connected to the ends of the wire as it moves will register a DC voltage. The strength of the voltage will vary with the speed of motion and the polarity will depend on the direction of motion. We say that when the moving wire cuts the magnetic field lines a voltage is induced across the wire. This is the principle of operation of an electric generator. The potential gradient in the wire creates an electric field that exerts a force on the electrons and opposes their lengthwise motion. Shortly after the wire begins to move all electron drift ceases. The sideways component of electron velocity disappears and so does the mechanical drag on the wire. Some of the physical work done on the wire when it is just starting to move ends up as heat dissipated in the wire's electrical resistance. The rest ends up in the electric field. Essentially we are charging a small capacitor here. The capacitance is very, very tiny, and so is the momentary drag force on the wire. Electric generator. If we connect an external circuit to the free ends of the wire, electrons will flow out of the wire into the load. An equal number of electrons will flow back into the wire at the other end. The number of electrons moving out of the wire is small compared to the total population. For every electron that finds its way out of the wire, another one is ready to pop instantly into its place. For this reason the overall equilibrium is essentially undisturbed. The foregoing assumes the load resistance is high compared to the resistance of the wire. If a heavy load is applied, the electron population at the end of the wire will be depleted. This will reduce the electric field in the wire and encourage more electrons to drift under influence of the electromagnetic force. A new equilibrium will be established with a lower induced voltage but a higher current flow. The drop in terminal voltage is directly due to the internal resistance of the generator. Some energy is lost to this resistance and shows up as heating of the wire. Current flowing in the load consumes energy that is supplied by the mechanical force dragging the wire. This energy is converted to electric current and is dissipated as power in the generator wire and the load. Square wire loop. Let's take the wire and form it into a square loop lying flat on the desk. Position the loop so its edges are aligned with the cardinal (left-right, front-back) axes of the desktop. In the nearest edge of of the loop, cut a small gap and insert a tiny meter so we can read the voltage induced in the wire as it moves. The uniform magnetic field still emerges vertically out of the work surface. Slide the loop left and right. Electrons in the front and back edges don't drift because the force shoves them sideways against the inner surface of the wire and they have nowhere to go. Electrons in the left and right edges try to circulate around the loop. But while electrons on the left circulate clockwise, electrons on the right circulate counter-clockwise, and vice-versa. The net circulation is zero and no voltage reading appears on the meter. In fact, regardless of how the loop moves in the field the net voltage is zero. This is true if it slides side-to-side, up and down, diagonally, or in a circle. In every case the motion of electrons in one part of the loop is canceled out by motion in another part of the loop. The only constraint is that the loop must remain wholly in the field, and must remain flat in the horizontal plane. Changing flux in a loop. Consider what happens if we narrow the cross-section of the field. Instead of covering the whole surface, assume it is restricted to a small patch six inches square in the center of the desktop. Let's make the loop larger -- a foot on each side -- and position it so it is centered about the field with a three inch margin all around. Repeat the experiment of sliding the loop, but make the movements small enough that the wire never touches the field. As we expect, no voltage registers on the meter. No lines of flux are cut, no electron drift occurs, and no induced voltage appears. The meter will deflect if we allow the loop to cut into the field. This is equivalent to the original experiment with the straight wire. Because the loop is not fully immersed in the field there is a net imbalance in electron circulation and a net voltage induced around the loop. The exception is the case where you put one edge of the loop in the field and slide the loop along the length of this edge. Since no flux lines are cut, no voltage appears. You can also generate a voltage by picking up the loop and moving it about in three dimensions. How much voltages you produce depends on the relative orientations of the loop, the field, and the motion. If you attach the loop to a stick like a lolly-pop or a road sign and spin it about this axis, you will generate a nice sinusoidal AC waveform. Of course, if you slide the loop completely out of the field, you'll be back to the condition of zero induced voltage. Rule of electromagnetic induction. We can think of this situation in terms of enclosed flux. When the loop is horizontal and completely immersed in the field the net enclosed flux is constant regardless of its position. For every flux line that leaves the loop, another one slips in on the opposite side. A voltage is induced only when the loop moves in such a way that the net enclosed flux varies. This is the case when one side of the loop is leaving the region of the field. It's also true if the loop remains in the field but rotates so that the number of flux lines passing through it changes. This leads to the all-important rule of electromagnetic induction. The rule states that the voltage induced in a loop is proportional to the rate of change of flux in the loop. There is a minus sign in there as well; a positive change in flux creates a negative voltage, and vice-versa. (This minus sign is very important, by the way, as we will see later on.) The rule of induction applies when the loop is cutting lines of flux in a constant field. It also applies if the physical extent of the field is constant but its strength is changing. This has a profound implication. It means you don't need physical motion (as between a loop and a field) to generate electricity. All you need to do is modulate the strength of a field enclosed by a loop to induce a voltage in that loop. Microphone Placement Microphone Placement From [email protected] Sat Jan 20 15:43:32 CST 1996 From: [email protected] (Joseph Pampel) Newsgroups: alt.guitar.amps Subject: Re: What is your best trick for miking an amp? Date: 20 Jan 1996 05:34:51 GMT Distribution: world Kevin: Here's a couple old reliable things to try.. #1 be sure that your close mic is off axis.. never have the mic pointing at the center of the cone. Try for about 45 degrees off axis. Move it around as well, tiny differences in position make big differences in tone. Try the outer edge of the speaker as well as the inner cone area. Might even try above the amp cabinet, or off to one side. #2 have a good room mic far away from the amp. Say you have a 57 or a 421 up on the amp, have a u67 or a 414 back against the far wall. Gets a real nice natural "room" sound, and a little "room" can really make a guitar sound.. Of course try and record in a :large: room. #3 use an array of mics in front of the amp. I know folks who swear by this for micing Vox AC30's. What you do is take advantage of phase cancellation etc. and set up say 3 or 4 mics in front of the amp, at varying distances and locations (relative to the front of the amp) you have to move them around a lot to get the tone you want so it's a pain to set up but the results can be amazing. #4 old trick - put a mic in the rear of an open back amp to catch the "thumpy" low bass. might have to play with the phase switch on the desk to get this working (or move the mic in front around) but you get some real thickening this way. #5 if you're a reverb fiend, record the amp in a bathroom or a stairway, or even a long hall. .. just experiment and have fun. Joe NOS defined NOS defined From [email protected] Wed Sep 14 23:10:27 CDT 1994 From: [email protected] (Brett McCarron) Newsgroups: rec.music.makers.guitar Subject: Re: What's NOS mean? Date: 14 Sep 1994 19:04:18 GMT [email protected] (Brian Minsk) writes: >What does NOS mean? NOS is the acronym for New Old Stock. It's an item that is old, but ios not used. Since it never sold, it's technically "new" even though it may be several years old. I have quite a supply of NOS novelties and magic tricks >from the 1940's and 1950's, for example. I bought them from an antique store who had bought it from the original owner who had the items stored when he went out of business. Besides being virtually unusued, NOS music items have additional value since they often come in the original packing, all instructions are there, etc. etc. >Thanks, >Brian >_____________________________________________________________________________ >Brian Minsk Center for Human-Machine Systems Research >[email protected] School of Industrial & Systems Engineering >voice: (404) 894-4318 Georgia Institute of Technology >fax: (404) 894-2301 Atlanta, GA 30032 Stage Placement Stage Placement From [email protected] Sun Dec 8 12:57:19 CST 1996 From: "David Papineau" Newsgroups: alt.guitar Subject: Re: Amp Placement on Stage Date: 8 Dec 1996 05:47:29 GMT I would go with #1 unless your guitarist is very restrained. 98% of the time the end result is like the one you just saw, "sounded like shit" Another trick is to have like instruments on opposite sides. Example: Stage Left - Bass and Lead Guitar / Stage Right - Rhythm Guitar. This keeps the stage from getting too muddy. Rhytm Guitar and Bass often times are playing the same thing or something similar. If a guitarist can't distinguish what he is playing, he turns up. It is a proven fact. Then the Bass turns up, then guitar, then Bass and so on and so on. Having a Lead and Bass together helps alot. I have even tried turning the amp slightly back to the stage instead of straight across. You can effectively "wash" the back of the stage including the drummer with very little volume. The sound is going away from the audience and improves the overall mix greatly. Just a couple of things I've learned over the last 12 years playing in bars. I'm sure there are other tips out there. I would love to hear them also. Dave . > > 1. Face the amps sideways (from the side of the stage pointed towards > you in the middle) This being so the musicians can hear themselves, > yet not effect the house PA mix out to the audience. > > 2. Point the amps out into the audience and re-enforce the PA with > your amp. > > > Any opinoins on what works better? > > Thanks, > > Doug > > What Are Optoisolators What Are Optoisolators From [email protected] Thu Jul 1 09:49:29 CDT 1999 From: "Gil Ayan" Newsgroups: alt.guitar.amps,rec.audio.tubes Subject: Re: LDR's - what are they and where do I buy them? Date: Wed, 30 Jun 1999 10:32:29 -0700 X-Posted-By: @138.13.114.187 (urula) X-Mimeole: Produced By Microsoft MimeOLE V4.72.3155.0 Xref: geraldo.cc.utexas.edu alt.guitar.amps:187172 rec.audio.tubes:127063 Jeff Stapleton wrote in message <[email protected]>... >Mesa/Boogie uses LDR's (apparently some sort of light triggered switch) in >many of their circuit designs. What do these thingy's do and where might I >find them? Go here: http://www.egginc.com/Opto-110/vactrols.htm and read all about the Vactec optoisolaters (used by Fender, Boogie, Soldano, etc.). What do they do? They are a photocell which gets triggered by an LED, in essence achieving silent switching (hence the name, LDR - light dependent resistor). They cost around $5-6 a piece, and can be ordered from Newark Electronics, Magic Parts, etc. Boogie uses both the VTL5C1 and VTL5C4 types, Soldano uses the VTL5C1 exclusively, etc. Here's a minute-sized picture of the bugger. Good luck, Gil begin 666 vtlpic1.gif M1TE&.#=AXP"H`/<``````#,``&8``)D``,P``/\````S`#,S`&8S`)DS`,PS M`/\S``!F`#-F`&9F`)EF`,QF`/]F``"9`#.9`&:9`)F9`,R9`/^9``#,`#/, M`&;,`)G,`,S,`/_,``#_`#/_`&;_`)G_`,S_`/__````,S,`,V8`,YD`,\P` M,_\`,P`S,S,S,V8S,YDS,\PS,_\S,P!F,S-F,V9F,YEF,\QF,_]F,P"9,S.9 M,V:9,YF9,\R9,_^9,P#,,S/,,V;,,YG,,\S,,__,,P#_,S/_,V;_,YG_,\S_ M,___,P``9C,`9F8`9ID`9LP`9O\`9@`S9C,S9F8S9IDS9LPS9O\S9@!F9C-F M9F9F9IEF9LQF9O]F9@"99C.99F:99IF99LR99O^99@#,9C/,9F;,9IG,9LS, M9O_,9@#_9C/_9F;_9IG_9LS_9O__9@``F3,`F68`F9D`F MF68SF9DSF MF?^9F0#,F3/,F6;,F9G,F MS&8`S)D`S,P`S/\`S `SS#,SS&8SS)DSS,PSS/\SS !FS#-FS&9FS)EFS,QF MS/]FS "9S#.9S&:9S)F9S,R9S/^9S #,S#/,S&;,S)G,S,S,S/_,S #_S#/_ MS&;_S)G_S,S_S/__S ``_S,`_V8`_YD`_\P`__\`_P`S_S,S_V8S_YDS_\PS M__\S_P!F_S-F_V9F_YEF_\QF__]F_P"9_S.9_V:9_YF9_\R9__^9_P#,_S/, M_V;,_YG,_\S,___,_P#__S/__V;__YG__\S______P`````````````````` M```````````````````````````````````````````````````````````` M```````````````````````````````````````````````````````````` M`````````````````````"'Y! ``````+ ````#C`*@```C_`*^Q&DBPH,&# M"!,J7,@PX:R&`AM*G$BQHL6+&"%&S,BQH\&-$@-Q!$D0),F!)SVR2OE1I4N4 M+%_*G$DS8\R2$!,BPGG09$Z>+7E>$^BS9\%6* D&VK@484JF$6_^7"BUIE6% MT%Q6+5IPZ$5K3D4F!;IS+"NQ*]$F3)F5(+2R715&C6OTJMV[$JO.;!O4+-Z+ M`ILR+ KU+T*DADOJ30)=5J+?B0(%A6?%?2K3E4H"RGC4.+'LT*\<#/ M!ZT)`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`\U2RJT8+96 MHI#1Q>NQ]H7+V.I;NQKQ!)#.S*^B$JTWD$/E?KG2A$URS&;'*Y(,,@HGTSR MO3KC:V_%#/FK$&X$9EODQBGG2C/#B@6"6HL3\;?8D+,*.9'(O)9LLLX\=VUO MTB8>W6Z05)*8H[<*6Q3RN"6S[3/7$/=\LHM**;2*T(Z6A_3'7M[__*_(/(]+ ML=M=$_ZVM(E:.%ZIC9K+=U2?*>MWPF?M_?.^6X\LL<^#8X[OE 3!!12P252E'S+>:RJ$[?M]=>Q0QSRUQRFRPKCK!"]M]4T?68VEZU_9-Z/-"J% MM>:>;SUXSJ1C_C6DM ,]WFJ(E/I06VN#[9[I_4%T+,6S:WXX],P[?V^S/Y<. M?#37!!<((H7J$:=DQ2<$_^3W.0NX^7(K',G>QCE?+>59A:J;`ED!%IGQJ13S MHQN;\#*40[#G-*8@V/@NE[GR28]V!*Q>L%R4M?0UK#J!X$*D1 *7!S'F&F9K MD2E00QW X(]I,+(6`C<7/?()"WK/TYKC_RJWKZP)3$B N *RPE.F@D"-3'4+ MA!XZI[X0IL^')B,AW(9EN),)+F7-4J(5(&@0WK%"="_\UJX*U06O'>Z#'2SA M^>!T#:X!T'/!*B$'5S5%+A0D@P4+W;QT!9,+*D1XEMJ5INS7!3VT48"VNQS@ M",B^/DF/BH.CGN Z*#HTMFEA%^/20BI#^8U4C666_]JWODA]\6+TV M1D0KNM)7#@L M%R"!CR:!:"36"* M"2)(,1UY(C:G:,2%-K92;N)J9!OY)%!'PLF1]N/F$,U'$"]2CXBQF]L:_<>G M@?A&-@M"A GN>&"_11@DP"$GT>!&KM>$)1^CE5 ` MYI&9*\2 MRWR3_&+@R!<]/+XR@;Z9)MY<,B2,7/-O<"HF0F'ZSV/N":J/;&7.!D*N5>'4 M58KLIC>=6< ^M4(L[A3+10<"R+39,Y0`(^$]_Z-V5H_$SJF,E*M-6^I//E+5 M@%)\I2O/R2M(L:VK0=VB.*-U%M5P%"G^6L4LJ&G8UB;/L%298.I&4]"X4O:@ MCW2JQ.)ZVG%V@'4@,""9G+50DW"TA.']5SI8$BR$8^"SC$0 M?"P`)6M0A/KPGV>A'^*::=<"SA%]XAIN.?5UJ) F3[%7,^LAZ?52/FX-JCPS M*+ZHBE-6/$&.FCRG5\T[.Y3MM%EB6UYB+V8*"XKD;O8\(?ZNT]B.7#:WZ6MK MJQZ9QU]Y%K.SK"BBMKK7J!;7KNS M'KP$KE__75($6G%'5ZF?!&%1]W:^>,5YP=*\E).A^1$2-P<]. M-L5AKB%B9/KMFOT\2UH.WW6229:J+IW,7E_M@98$60WO1&)*D+W+3W'[E5Q+ ME3[;7I93NS146S$Y60)O5K1%5&ZO6NRHCB[68ONI,$>,S+8VKC)[FTPH?CL\ MWEL6MZ^^6@'*N%IB#[,/G"YB7&MET6"U'7;&'C,RF&^KAYU -J[X,F@N@_7; M`(Y:IGD6KA?SB%?#Q7D@8Z5/A:SI2X- K;&JQB+;=C?5I]:WQY2FK&0%"#OB MBO##F^R3[;#&A3V4FQ6F7-0A:OS>_<06.=6<'XYU^^=4%7/':>VN4W_ESTW_ M?]K7FNW:KH=]T\J5N]R_.C>$U5(6=F-(TA:!"Y*[.S=SOK28_CZ M^W.SM.1FB>RH+5X!$/X2BQDM6@IT\1F9G))*3@8[F?E>\?%'%?.I^I24!\: M<0F\::$1=;L>KK=(`I+%:JAYB*U\S,JB"81PTEO$.*;*I6NM;9ASK=OJH=.( ME:R7J];,PT@*BQ405HIP6&%=A\LD1)/"D^;:BE\NXI2*![VC/]ELTUWM=- M#-;)<4=B-ADW4R$.$8`:%M=CUBR]^95E[,IO3#_W,@!-G5Y.VLH`5U!DL#: M`[ `0;H]H%LL%I3S3IH;848I"+E[^B>G85K +N-X_V2K'"@C,T?T`&>>3\HL MY\CHRB= .!-.*T8S%TH5#9%D$!IU/J,TGU@\'$GZ9079L>33>K*U\OOB.<;P M6B]NOXTW4XND*[+,=JJ^0YMWB.@^2[4P!B.]&.W.;,?6G$[MY%8.5.?_M$H$ M97[UQG/X)F)NHR\D-RYY0W/<%BR6=P4^YBH[`4B+8D8OI'A,@EGD4GY6\&7Y M,G#YY7&YE2JY)&YS@TOD)#L.:'17P 5Z\'E[P@6!8&ZB)Q*E<@BKD4%%%7\4 MU""A`DX#=6]3I%A8Y&_D!V1==#_V M$F/6%6.01B66HC1!F'=/5?]K\Q,(V25R/B M]L,%GP<(4& %HK MC 1!]K,3'&@OWE=MBJ1-7]9FP85.7N=Q260%I$=ZU79PGV<_,E!78F$*99%L M%%$L35,1I109,Y%3_51I1\97J])&,U=$E<2$=W1J._1&FM.'GR>#>0>-=;4J MYV9!C,-Z-=%+&@@\"7$LX\=*QEA@-74O>L)/9)9 MNZ.%\*46IH2++4%2?M)0LE9I@G-OPV)IC&0HI=!(K&!ID5*$S5BE^=!4,@V M@,#_`EAH!56P*BO *C% +@B"%,'!(QX%3+"U6()Q?ZD2=Q;A=H]6B:T'*9Z% MA)&5>R)6.:Q04PGD2$0T1;8&7(+69;(30H?3AUOSA_"8D4+9*GIP1CFX.P81 M?9%H+6I!$NL3*-L(+T(B: 66+Z72!06Y0O[F6 MBW!2E/ XC'^$E,X57PNC/.WE*9TB15T7415EE%T`#0 M!55 AZT2BT4I`U4`!8YI!6RID0"#5'0#2"UG,=MT/(_8&**3AOJ68?_'+[$' M4Y>%AC,W7 (&>DM6:G BC7!RD58@FW!2D1@IF580F2P@_XO+9BNJ%ABR8)DP MTX" M*0/?B9MMN4LNTH4IN1VW@RPS,A1$8E*N=A_9]([&5):_"%- )T+,LTKO6'-[ MU"J[606[N9MU99NKDI&L8J 3@VSMM(6(V(U[TWLWTFRYP8G+`X] M@(314EGX:8;:29L%6E<7R0)I"8_C2:!KN:"&L@KXD2HT.#Z70J&A`1>IV6,8 M*EH[)8!@MG?_>5OMJ)BL0INTB:(H6E=04)$$*@.3:9LDJE/&0V0=9RAOMI*P M)A/8IT!S]E:65YZR9"C9HWO:1_][PTAQ1JE*>C6-49J@=46@CZF@<**6L@@T M1P-R=,894TE/+O*C>ABB;1,K.,AO7+9MP$A)Y=DJ;2J;1VJ; M#12A^;,6>YJ>*T$_NZ=AN"5[^0(P^*EG!]AG]96HBDJB47JDY/*'3HJ@XAF; M M M)BJK\$J;`FJ;+)"D+)JD2VJK&9FB=>6DV-JB^W(%:+<:%R,9,^11;E(A#+,5 M2:49(;?_8:Q$I*=*DUS#DY_%3UTPGJBJJ. ))TEJK0'**E @FT*YFT] I['* MG;=97@4Q5I>J&+/2E.^Q(FM35YXZC>::E]LV6:URLM$*GO/JL11IKZL2M$!; MK:T"!3&@M =:M*MRLAK;L? XL"3D&XG5C9K*6#41#;(`/UWK%3'S.I&R9=6& MJN.HHP9H6_T4M:QBJU8PGDSJM-8*KT?+*@'*H@"[EK;*F)!:FWC+LO6(.G2# MC]]:(6,A-24!/T,A"YV!&AO47I:861(+J/[GB;R%;WE9I#^;H$5)LK8:LG:K MLO\*K=E:M$+YG9&)M/!H(8?P%C/TLD[!$@P+,]?PM5][IVLC_Q]O@31U"K$[ MHZQTJ['CJ9:0^:_%^Z_DN2I$2Z\7^8=_>Y&T2:<5R99+RIL`(PA6&PU%94H9 MQ+V0AA^(2Q"VP;B*FRLKY#VY8EB&6:=8M+%]&[S2RKF2^:R.2;3+VK2VR;8D M&K=UJY9_BRB()Q)#A;W=&Y<$@8AH(9R+U:L#D5(P\QGDNX5O=BP3O'B4=[/V MM2\:&S=MJ:I)FZW^*IM-FIM/"H_.N[ELX[/QBZK-UV@+9C %@7A-V7J()2L, MP;7P\4=K1*,TB+6:F5GWN;&92[?W6ZT:2Z>TR98(NJ^2B:#\2\0&^JA$[*I$ MO,+L=+4N`@TQ5AN(I3@NLHB$T;A, M??N8I0NI%=F\TYJR2ON'CWJ1*-O$51R+%WFM M.=P98XPH,UH@AR"A82B)@5*PS.B^;$HNV4J]WEFB*LL"L+JL46JRTZC"1_RF M>=M2JX>]V!LZI=)PWLIVEXG+9(-/-@-&1!8(C"P>]\1MJ"K(FJND@)R63!NI M35N4]VJ;2TJM%>1,U4;3#L(LQLH;!GDS" M0RNZKYRO%/FD2)R@QIR;CQF+A&RD? M'(,V*5FPX0QB4>::SF[ZOL7+KX,O*0KE(PIIR1KNM/JQ^5)R/XLLFWY8"R4 M-Z7RFT6CQG(17#Y"2%9S,?B&SJL,CU+\MMSIK^X,C[M)HBPJF_:LEOE[O\/[ MM$#=KS7-0J9@M6A1%CT8PV?_DBRB1%8J*64;!*B)JI9JN:)Y2Z^0RL>;&ZG? M: MN\QPZJK?&;W'/)MXN[1$_9V3*L4?F]8;>T9TED%2AG9_! M_6H,78]BJ] MHHTM#1X6X\4U_DPC9^B[<]8S=K/ZK%0NK2,F:UMVM=PLK0&ZL1)6\Q6[+Z0 M?8LGX7!EQJW0*ZM43)XB3)%8 M+;5[_UV;TOS8%W/)\4>+=X.-3CVA)QF&"=S0#(>!HZB=GLRO[VW/<'JB:UG6 ML;F;BUVMD@BVAP(Z]:Z,);+CFQ656&/" [.PJU ;7T0 M60'149NO)%J]10FM;AK/0FN;2RRT>PVGROO>^"VR-:W:2%Y.] M,^QRCV*2(J623@3,9]%\"^;%E)$4V0+1:KFJRINB.M[$D_FW3RR4;.G'3U"1 ML?BQ&IN6/DO8*NN8Q^O)1N@HF$F(W@I,-@$2Y1$8P)TK%G2/7#Y!UP`-LS 4 MLZ#HW<%-QPS=R7OC*WS?5LR6 M%GF*=DQ]RYA]777-C6^9$UZAZ-# %)-;W7(KZ7Y;Y-,KL@AZD409W:=+O CJ MLWQKM!6YQ"7LV*;^2'ECM3ZH%M;5U.=R$Q-V'8V^[1E"/T"LIN[JM&PYGHC= M*M1MT[*IS.8.L'L[JV$.J;1*O%T=POD-XN42W+FR=+/.T.F[A2V,[ZV7 M+;<^G+!BA25M3D, MV0BQ>JP@N+A]->Y9N$OIYR0B*9IA?9(L,^)6)%G1+,6MN8Y9OTVKLE JK>^N MZ^$YV*D=WTZ:LD,]H.^\\V"-JGK_)HJ*S(.9:5$-*NL=PQ\S7&=@:_ KX>B_ M+!)K!UNS,#+E9@43*>K0'+_._,JF+9F67I%Z$,]U'-+J;:!)7,2)^E]NV7O= M>C%OK?+]SMGG`K,Y_!#CDY*JKI0>K\[,'*E1#-O+W.%%KKDL,-;8NLSP&NHA M[ M[LH]_[9A?L?X/9E.6M-'WF>&>A:M7R D_^K:72*Q6Q&@OQ+E*\DTRWE8O.2' M;RB/1'I$JI:Q3YZ6WO&36;IE+M**'_QM"]+IS&-$1R"'S^>VF! M MF]M#\?SD_\V>"W$P*M?9N3ZM`&%%X$ K+ 3*L%)%X!.",:Q &:C0X4."%:T@ M' A1H<6-"RUBS%@QD,6!@0+I864R):N5@5BZ1,22Y:J8,FW>Q)GSYK5K.G-& MD]53:#2>066J-.DR9TRE-6TJ?9G2RA6255<,9)A0(!205JX^5"CC"4:(!&64 MC0&E8Q60"*$XA-@59$>27*H*[")P)"*D*5TJ_I3L4R>.W7R M;"STFJQH+Y/Z?9J9U>'-*U M39U;X![=>O1:P0PX.#1!I5JMLNDTYZI6B6WVQ-GX,2O(T'D2I?_>\N\UE]QO M)@XT"[#WSX%+=2GUVZ[NCG$9TA[XU6O%*F5#"K1]5S['J;IU=]$#O;X"0 ME@YAI28$#?2IL,44DRZZ:X ""C+JO.MK,? ,T\P\T48:R3_8!,+MOJ]DV^HB M@EA8BT06K M0:P`\*Z-WJ(H-1DZZHHM_E3$KXK\: 0S-Q!',A(I`S=D!4$DD8QL2"$C:^E! M-)?:3+E 2@$MJ4"N" 00`*_@@C?_6OOJK(MD^^JJJPRJ+X;6[@LS4MT"%8@J M5H#+$#!KQEOS1^B$O# HR"B#3J4UG4/_C$,E/[3")$! + TUB[Z\:K424[// MO]=T*^O6W 0-]%5,`UL).58<[#19EJJ;L-E2B556,\.80NS#)IM\TJ0J1BHM MMRF]A#&V*VU#,2&,;+/Q18_BTPT^@^"[RRX06[TL)U.4B[;342V4Q93+U-1I MSL5B*@4F:_74.E#"",4?=6JH!'G.^BCLKB*5- Q`Q,N MS9EP0C5?"2.L5V6?7#J,VH(1#D20P6I&ZLX]NZVJW'"KLN]1&3'NR$88MR0I MUXIXDW>O`7L\)!J!69+Z9)P$L>;!3R]\B0M3?038I@5Y/&1#DV;F"^$R$63U M"IY=(_$N=:^L_W+%@\HRFF-$-Y8T1'E;I?=.OIXBCT%DCTRS,E9:T? MT)2M%U/\ILI9Z?>EPD1CI0N_!C2N_+\^HVDK/)3B]$4!Z(-H_HPGN]+CL-D M6J#UK @TT)&AQ=-EWQDC+]FP90H;,&@..;-,8CE7,K243K/(Z-5LBSCICFN, MR"R"3IQTMY'VT#WP'.-4]259!'LP;&/S#?)WXAED:4=3RL:S?@=)[M$E!ETZ M1)! ;O](1%(WF^P1L&ZPVX_1?%85GOD&<*2A5^ ^X[RCL 01T5 3_! 7L-\5 MA27GRTD@KC$_5FAP?R7D44MH$AJ2*85M/?(,_Y8WLP>21'8*4=I==O^5&]G= MQ6V5PAU5QL2G`2TOAK- WZDPR!B9:# G6X/BY72R1)RH*6IJ8EZJ/L,*:(RG M9$8L8H@LHA&!&*V'5<%-;+AT&Q']$$J VP/-Y&A!"N+$B4ERWQ,GAZ0[(DXI MFWM)%U\R"\[ M`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`T($2\4;RU"& MC3--N2AG7-9'E5GH@RESG A3LMOGC >+$%TE?0WCS)1PQR7&TE]'@Q,BT#XD M+;#9#TCUP 59S>M:)AG M#&*.L32(WI+E[[#W[&:!0_H?T^QU3(!@!1?PA!(]Y5.P2D*,@,EWF-X=!KJ* MQ6ED07PA%Z)PFFQ=LF*<.-Y 4&NK)K'N=:W@FS%%T*6>ZPM+5[):`J6DJ?]) MI&T@H-G,0EKC?@&UTRS6Q[B;WF2WD8T&-K5SP[!4 M[R@EZQD'D;*;?EFD?Q@<*S\%Z+MX^LN]\"1FF%'KL&66'T;ME!Q2&]9J4M9M MIT#H9N!",7C7^*E^MUE%*F+M?ED##W\#4;E%"QAY,.5 M4"HZX:QVG BJL"E.B.6BOO#[2R9 M1T^[! B"6_YLJP`$(F*JEBF?I!94A MDQ,*(J!FJU8Q`05$8Z'_JE+'P^F 1FT\V!;YJ4_L M(X2?DJU0[E3*D+QML\+/*<@YJCH1XZ],;CEWX-/3S*[,4I)1D#!DJVR&U10S M-C-\LHG1 MQ7%W5=:?F;HJTR1R-H5.QC"']5DL?"$9)V)>3+E5]G7!'"<[$XI6U3[(WLQ8 M M>>'TY)@GFW#VM9R/?+RSO7:KIE?NFG@//Z2;H[)QI&#<0\ MWA:.FARTUEIGK3 `?DI#/K^3+V]#R/8^X?J//ORCL&4;IZO]=?23AV(.:PJV M+!4^\:*"Q7 6MOR![J/^;H*(^"/5FM3AO1#Z/B1Z'.%B_R*M MXB9]X@P#B1D)1#L'B9E5$B^H MH:_=,HZB;Y*R%=XZ^CRCS4PRQU"[@_ M\C%:*H476C0$.3MQ4\(F,QG&HSUET:8HLT$8/*KED),74T 2`@Q9\*)#F*U# M(@]#\B*S,KGFN[S*"(3XT[_ M6 MM+W*(+Q349FP,J?P$K@J7+16K%$Y@ F;#-N@<@N;\+LF0.R4Y-*M@.(I+O)$ MR6,%3+2&7^Q$7APW&SRH9ZH)5JHVYBBDLE.\^/$URR(?H=(,G&.N#>H1;!H_ -^/I#(/$)/KN&@ ``.P`` ` end What Dealers Pay What Dealers Pay From [email protected] Fri May 29 12:41:00 CDT 1998 From: [email protected](Lord Valve) Newsgroups: alt.guitar,rec.music.makers.guitar,alt.guitar.amps Subject: Re: ?Dealers, Prices, At Cost, Markup???? Date: 29 May 1998 07:36:11 GMT X-NETCOM-Date: Fri May 29 12:36:11 AM PDT 1998 Xref: geraldo.cc.utexas.edu alt.guitar:264263 rec.music.makers.guitar:207749 alt.guitar.amps:107643 In strat writes: > > >I am curious to know how much do music stores (especially large chains or >stores such as Sam ASh, Guitar Center & Musicians Friend) markup the >prices after buying them at cost. What is considered at cost normally for >guitars, amps and the likes (strings, tuners, etc..). I had a friend who >told me after speaking to someone who used to work at Sam Ash in the drum >department, that the drums were marked up 110% after buying at cost. I was >wondering how much these stores normally buy the equipment for. > > Lord Valve Speaketh: I own a music store. This is the straight dope. Things like accessories (cords, strings, straps, etc.) are usually marked up the highest. In the quantities the large chains (like Guitar Center, Sam Ash, etc.) deal with, it is not at all uncommon for them to buy strings at 15 cents on the dollar. This means that a set of strings which retails for 5 dollars is bought at wholesale for 75 cents. If they sell you the strings at 50% discount (2 for the price of 1), you pay $2.50 per set. This puts the markup at 333%, for a gross profit of $1.75 per set. Big-ticket items, like mixers and power amps, are a different matter. Many of these items carry a 40% dealer discount, with some at 50%. At a 40% discount to the dealer, a mixer which retails for $500 costs the dealer $300. If the dealer sells the mixer for 25% off, this results in a gross profit of $75, or a markup of 25%. The mega-dealers often get off-sheet pricing; for instance, Guitar Center gets a 9% additional discount from "end-column" pricing. This means that a QSC amp which wholesales for $500 (the price *I* pay) costs Guitar Center $455...thus giving them a $45 advantage when selling the unit to the public. Guitar Center, however, has *no* service department (at least, the one here in Denver doesn't)...and my store *does.* That's *my* advantage! :) The mega-stores can often cut deals with manufacturers for special "one-time" pricing...for instance, Sam Ash might cut a deal with Shure on 5,000 SM-58s at only 75% of the usual wholesale price, and then sell them to the public at or near cost. This brings customers into the store; they are also going to try to sell you a stand, cable, windscreen, case, etc. with the mike, and those will *not* be heavily discounted. Some lines, like Ashly, for instance, do not provide off-sheet pricing to *any* store, regardless of size. Ashly has one price for 1-5 units, and another for 6 units and up...end of story. This means that prices on Ashly will be fairly competitive, wherever you go. Many manufacturers are now setting MAP guidelines; "MAP" stands for Minimum Advertised Price, and no dealers are allowed to advertise a MAPed item for less than the set price. (This doesn't mean they can't sell it for less, just that they can't advertise it for less.) Behringer is one line that does this... so if you check the same item in your Musician's Friend, Sam Ash, Music Emporium, and American Musical Supply catalogs, you'll see that the prices are all the same. *Ask* for a better deal on the phone, and you *might* get it. Hope this clears things up... Lord Valve Website at: http://www.freeyellow.com/members2/lord-valve/ "I got the chop...I'll never get popped." - Tower of Power What Is Tube Glow What Is Tube Glow From [email protected] Tue May 14 13:11:56 CDT 1996 From: cynic <[email protected]> Newsgroups: rec.audio.tubes Subject: Re: Blue glow in output tubes Date: 14 May 1996 06:44:27 GMT I am amazed at the ignorance of so many of the posts here. Blue glow is caused by one of two things: a) fluorescence due to electrons striking an object. Often, stray electrons will escape past the plate (esp. in cheaper Chinese tubes) and strike the glass envelope, producing fluorescence. This kind of glow is harmless. If you can look thru the slots in the plate of a 6550 or EL34, you will probably see the inside surface of the metal plate glowing a similar blue. This too is normal. b) gas ionization. BAD. Many older tubes, such as type 50 triodes, have soft vacuums and can sometimes show a bit of this. Cheaply-made tubes (most Japanese and Chinese types, for example) were poorly evacuated at the factory and can have gas glow inside their elements. ANd occasionally, power tubes can develop a slight leak thru a glass-metal pin seal, allowing a tiny bit of gas in. Ionization due to air is nitrogen and oxygen, which gives a purple-pink glow. It is distinctive and very different from fluorescence. I know this because of years of experience, and years of doing research on tubes in engineering libraries. There is an excellent discussion of this in the 1939 Sylvania tube manual. -I HATE COMPUSERVE (but they are cheaper than Netcom) What JBL Means What JBL Means From [email protected] Sat Jan 6 20:36:51 CST 1996 From: "Mark E. Huss" Newsgroups: alt.guitar.amps Subject: Re: what does JBL stand for?? Date: 6 Jan 1996 04:06:19 GMT Mime-Version: 1.0 Content-Transfer-Encoding: 7bit James Bullough Lansing >from "Insight:JBL - An Introduction to James B. Lansing: The Man, The Company, The Product", an *old* promo booklet (from before Harman bought them). --mark What are orange drops What are orange drops From [email protected] Fri Sep 8 10:56:02 CDT 1995 From: [email protected] (Dr. Nuketopia) Newsgroups: rec.audio.tubes,alt.guitar.amps Subject: Re: Caps, caps and more caps. Date: 7 Sep 1995 16:17:22 GMT Distribution: world Mime-Version: 1.0 Xref: geraldo.cc.utexas.edu rec.audio.tubes:982 alt.guitar.amps:3445 In article , [email protected] says... >The "orange drops", as I know them, are polyester film caps (or >polypropylene film) made by Sprague (and others?) > >They seem to be prized by guitar amp technicians, although someone with >more experience would have to explain why. > >Remember, distortion in a guitar amp is not necessarily something to avoid. Yeah, orange drop is a nickname for Spragues polyester film caps. Tantulums are useles for audio coupling and what not. (when I was fixing electronic equipment, tantulums seemed to fail an inordinate amount of the time). Orange drops are popular because they work well, are easy to get, and not very expensive. You can use these in hi-fi applications, and they sound good, but there are better polypropelene caps for that. Orange drops have a nice clean smooth tone, versus the the muddy sounding and unstable old hollo-wax paper caps originally used. The film caps have much better leakage and inductive characteristics too. They will probably outlive the amplifier and the musician. I don't know if anyone has tried a WonderCap in a guitar amp. I think it would be overkill. But it would probably work very nicely. -Dr. Nuketopia Technology Director of the World-Wide Monetary Conspiracy Opinions strictly reflect the party line From [email protected] Fri Sep 8 10:57:11 CDT 1995 From: [email protected] (Mark Garvin) Newsgroups: rec.audio.tubes,alt.guitar.amps Subject: Re: Caps, caps and more caps. Date: 7 Sep 1995 12:21:11 -0400 Xref: geraldo.cc.utexas.edu rec.audio.tubes:981 alt.guitar.amps:3444 In <[email protected]> [email protected] (Chuck Harris) writes: >> Why are the orange drops prized? I expect you are talking about >> the tantalum semi-electrolytic caps? I feel they are no good in >What you say about tantalum's is true, but the "Orange Drop" is a very >old (circa 1960) polypropylene tubular cap made by Sprague. Regarding orange drops, the 220's, 225's, 6ps, 4ps, etc are polyester (mylar). The 715's are the polypropylenes. They look almost identical. 'Prized' varies from one engineer to the next. I've heard discerning designers express preferences for old paper caps. Regards, Mark Garvin From [email protected] Fri Sep 8 10:57:31 CDT 1995 From: [email protected] (Lewis King) Newsgroups: rec.audio.tubes Subject: Re: Caps, caps and more caps. Date: 7 Sep 1995 21:32:44 GMT Distribution: world Reply-To: [email protected] In article [email protected], [email protected] (Mark Garvin) writes: > > Regarding orange drops, the 220's, 225's, 6ps, 4ps, etc are polyester > (mylar). The 715's are the polypropylenes. They look almost identical. > Yep - darn confusing too that both types seem to be called 'Orange Drops'...the 715s are sold by New Sensor and they call them 'Orange Drops' in their catalog. (BTW- the Newark catalog confirms the above...that the 715s are polypropelene and the 225s are polyester film.) LK Oh...almost forgot to mention that I'm not in anyway affiliated with either of the above referenced firms. From [email protected] Fri Sep 8 10:58:14 CDT 1995 From: [email protected] (Dr Distortion) Newsgroups: rec.audio.tubes,alt.guitar.amps Subject: Re: Caps, caps and more caps. Followup-To: rec.audio.tubes,alt.guitar.amps Date: 7 Sep 1995 16:13:33 GMT Reply-To: [email protected] Xref: geraldo.cc.utexas.edu rec.audio.tubes:985 alt.guitar.amps:3447 S. W. Wortis ([email protected]) wrote: : What's the consensus on capicitors in guitar amp applications (where : "hi-fi" may not be neccesarily desired?) I don't think cap type is as critical. Some of the best-sounding old amps use ceramics (gasp!) as coupling caps. For my own amps, I just use regular polyprop film or silver mica, depending on the value needed. : I know the "orange drops" are : prized but what about polarized caps? I assume you're talking about power supply filters. I have found the Japanese "Illinois" brand of 'lytics to be quite adequate. Again, there's no need to split hairs so finely when talking about guitar amps; we don't need our power supplies to be as stiff as the audiophiles require. If you look in the catalogs, they usually give figures of merit for the 'lytics they sell. You want a fairly low ESR and a wide operating temperature range. Most 'lytic figures are given assuming 120Hz of ripple, so be sure to compensate if you're looking to replace the caps in one of those really old amps that used a half-wave rectifier (with 60Hz ripple). To make things even simpler, the 'lytics you can get from the usual suspects (Mouser, Mojo, New Sensor, et. al.) are just fine for guitar amps. Of course, watch that voltage rating... What is 6V6GTA What is 6V6GTA From [email protected] Mon Mar 18 12:16:23 CST 1996 From: [email protected] (LarrySB) Newsgroups: alt.guitar.amps Subject: Re: Attention 6V6 experts - advice wanted!!! Date: 17 Mar 1996 23:40:51 -0500 Sender: [email protected] Reply-To: [email protected] (LarrySB) The 6V6GTA is identical to the 6V6GT, except that the heater current is controlled during warmup. That was a concession for TV set makers that used series filament circuits. (all the tubes string together like christmas lights) Other than that, no difference at all. -Dr. Nuketopia Technology Director of the World-Wide Monetary Conspiracy All Opinions Strictly Reflect the Part Line What is Bias What is Bias From [email protected] Mon Jul 8 09:16:33 CDT 1996 From: [email protected] (Mark Garvin) Newsgroups: alt.guitar.amps Subject: Re: Okay, I'm confused now. (Re: biasing) Date: 8 Jul 1996 01:39:37 -0400 In <[email protected]> [email protected] writes: > >My SF Bassman has, I'm assuming, fixed bias. I assume this because I >didn't see anything like minipots, but I did see some resistors. Hi Hal, Just wanted to correct a couple misconceptions about biasing terms. There are two basic topologies for bias circuits: fixed bias and cathode bias (or self-bias). But it doesn't relate to whether they are adjustable or not. The bias is simply the voltage measured from the tube's control grid (G1) to the cathode. In almost all power tubes, the cathode should be more positive than the control grid. This keeps electron flow within the tube under control. If the bias goes too far positive (well... toward ground), the tube will start to conduct too much current, the plates will show orange spots, and the tube may be damaged. The exact voltage will vary depending on the type of power tube, and even seemingly identical tubes can vary quite a bit. That's why it's nice to be able to adjust the bias voltage. Considering that it is the RELATIVE voltage that matters, there are two ways to make the cathode more positive: 1) LOWER the control grid's voltage ('fixed bias') --or-2) RAISE the cathode's voltage ('cathode bias') Fixed bias: A 'fixed' negative voltage is applied to G1 (first grid or control grid). This is usually derived from a separate tap on the power transformer. The term 'fixed' is misleading, since it has nothing to do with whether it is adjustable or not. Most high powered amps are fixed bias. Cathode bias: G1 (control grid) is kept at ground level (0 volts), but the *cathode* is elevated by placing a resistor in series with it. The resistor is usually from 200 to 500 ohms or so. As the tube starts to conduct, it will pull current thru the cathode resistor and the 'cathode side' of the resistor will start to go more positive. Naturally, as the cathode goes positive, it makes the cathode-to-G1 voltage look like it going more negative. In this arrangement, the tube reaches a point where the voltages and currents reach a balance. Hence the term 'self-bias'. Due to the self-corrective action of the cathode bias circuit, there is much less need to tweak bias. The tube sorta does it itself. Cathode-bias (self-bias) is also the way that 12ax7's in preamp circuits are biased. Though the voltages and currents are much different from those in a preamp tube, the concepts are the same. That's what those 1.5k resistors are on the 12ax7 cathodes. Another somewhat confusing thing: The bias voltage is controlling the amount of current going thru the tube. It's the current that is important: the bias voltage is just the means to control it. Due to variances in tubes, it is tough to set optimal operating points by simply setting the bias voltage to -48 volts or whatever. The better way to do this is to monitor the *current* while you adjust the bias voltage. Also, the mentions of current and voltage above all relate to quiescent (zero-signal) conditions. They determine how the tube is operating when there is no AC signal applied. The signal will drive the operating points up and down from the zero-signal bias point. >Does "rebiasing" this amp require actually swapping out resistors? Like >desoldering, removing, replacing, and resoldering? Or is there some >"magic" of which I am not aware (or minipots I can't see)? Sounds like your amp doesn't have bias pots. Unfortunately, you'd have to change resistors or mount your own pots. Trace the cathode pin to see if there's a high-wattage, low-value resistor there. That would explain the lack of bias pots (it would mean it's 'cathode bias'). >Please forgive the newbie-ish question, and don't worry, I'm not gonna go >stickin' my hand in the thing unless I know EXACTLY what's going on. Well, you're no fun, are you? MGarvin From [email protected] Mon Jul 8 09:16:48 CDT 1996 From: [email protected] (Mark Garvin) Newsgroups: alt.guitar.amps Subject: Re: Okay, I'm confused now. (Re: biasing) Date: 8 Jul 1996 02:49:30 -0400 Just read thru my post and thought I should clarify a couple things. >MGarvin: >The bias is simply the voltage measured from the tube's control grid >(G1) to the cathode. In almost all power tubes, the cathode should be >more positive than the control grid. This keeps electron flow within >the tube under control. If the bias goes too far positive (well... >toward ground), the tube will start to conduct too much current, the >plates will show orange spots, and the tube may be damaged. The bias is usually measured from the control grid to the cathode, so it will actually be a negative voltage. If that voltage is not negative enough, then the tube can overheat. >>Does "rebiasing" this amp require actually swapping out resistors? Like >>desoldering, removing, replacing, and resoldering? Or is there some >>"magic" of which I am not aware (or minipots I can't see)? >MGarvin: >Sounds like your amp doesn't have bias pots. Unfortunately, you'd have >to change resistors or mount your own pots. Trace the cathode pin to >see if there's a high-wattage, low-value resistor there. That would >explain the lack of bias pots (it would mean it's 'cathode bias'). Now that I think of it, you *did* mention that you have a Bassman amp, right? That amp might have a pot mounted thru the chassis, toward the front of the amp on the right side. That pot should be visible, though. The pot on many Fenders is not actually bias pot, but a 'hum-balance' control. It controls bias for only one of the output tubes. It's easy to change it so the pot is a true bias control, though. Post if you need to follow up on this. MGarvin What is Blue Glow What is Blue Glow From [email protected] Thu May 9 23:21:44 CDT 1996 From: [email protected] (Doug Haugen) Newsgroups: rec.audio.tubes Subject: RE: Blue glow on output tubes Date: Thu, 09 May 1996 22:13:47 Mime-Version: 1.0 X-GNN-NewsServer-Posting-Date: 10 May 1996 03:11:32 GMT I wish I was smart enough to come up with this on my own. I'm not. I quote the Sylvania Engineering Data Service handbook (those really BIG tube manuals): "Blue Glows are not tube detriments per se. They are, however, suspects in the eyes of many receiving tube users for a lack of full understanding of their origins. There are several types of Blue Glow which can be described as follows: Fluoresence: this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse effect upon receiver performance, and in fact, tubes displaying this phenomenon are particularily good with respect to gas content. Mercury Vapor Haze: is a blue-violet glow associated with those tube types which rely uopn mercury vapor for proper operation. In such cases, the blue glow should be evident indicating proper operation. Gas: produces a blue haze, generally confined to the vicinity of the mount structure. The proper function of gas types such as thyratrons, voltage regulator and voltage reference tubes, requires the presence of this glow as an indication of proper tube operation. Some voltage regulators use neon instead of argon and as a result exhibit a pink-orange glow. It is, however a distinct detriment in vacuum receiving types, where the presence of gas in large amounts can cause malfunction of the equipment." (Slvania Engineering data service, Vol 1, page 23, tab "general information", no date given) This seems pretty definative. I hope it helps! Doug What is Ground Lift What is Ground Lift From [email protected] Wed Mar 15 21:06:49 CST 1995 From: [email protected] (David Roach) Newsgroups: rec.music.makers.guitar Subject: Re: Ground Switching in Amps Date: 16 Mar 1995 02:52:24 GMT Distribution: world Rennie Selkirk ([email protected]) wrote: : In article <[email protected]> [email protected] (Scotty Stroud) writes: :> : >The center position (if present) lifts ground. The other two positons : >AC couple (via a capacitor usually .047uf) one side or the other of the : >power line to ground. : What does "ground lift" mean? And what is the function of the coupling : capacitor? : Thanks, HJB To lift the ground is to disconnect it, i.e. like there was no capacitor to earth ground connected. This is not the same as disconnecting your amp's middle prong of the AC line cord, which connects the amp's chassis to earth ground (it is not recommended to disconnect earth ground for safety reasons). The capacitor passes high frequency energy to ground while blocking low frequencies (60 Hz line voltage). The cap to ground arrangement forms a simple low-pass filter, with its cutoff frequency selectable by the value of capacitor chosen-more capacitance equals lower cutoff frequency (with this simple filter, the "cutoff" is actually a very gradual rolloff). If you were to gradually increase the capacitance value of this part, more and more of the AC line current would pass through it and the part would burn up. One of the things I'd point out about power supply hum (typically from poor filtering or regulation)-- on designs using full-wave rectifiers (4 diodes), the frequency of the hum is actually doubled to 120 Hz because of the way full-wave rectifiers work. So often, what people are calling "60 Hertz" noise is really 120. Dave R. What is Kinkless Tetrode What is Kinkless Tetrode From [email protected] Mon Feb 12 11:43:24 CST 1996 From: [email protected] (Martin Ackroyd) Newsgroups: rec.audio.tubes Subject: Re: What is a Kinkless Tetrode? Date: 12 Feb 1996 08:43:10 GMT Reply-To: [email protected] [email protected] wrote: : I've heard that the "KT" in KT-66, KT-77, and KT-88 stands for : Kinkless Tetrode, and that this is somehow different from a : beam power tube. : Is there any real difference? Who came up with this idea? There is no difference. Same thing. Here's the story as I know it... In the 1930's, Mullard had the patents on the pentode, so other firmes had to pay royalties. EMI invented the beam tetrode as a way to avoid paying the pentode royalties. But good ole EMI chose not to exploit it commercially. They had a patent sharing agreement with RCA, who immediately saw the potential and produced the 6L6. GEC [the British General Electric company - nothing to do with American GE] then decided to make an equivalent to the 6L6 and, in around 1937, produced the KT66, as a plug in replacement for the 6L6 GEC got very enthusiastic about 'kinkless tetrodes' and used the principle to produce rf valves [KTZ63, KTW63] that were alternatives to the rf pentodes 6J7, 6K7. My dad was working at GEC on radio design at the time and the above is how he told me the story. 'Kinkless' just means the anode characteristic does not have a negative-slope region ['kink'] like the original rf tetrodes from the early 30's had, caused by secondary electrons emitted from the anode, arriving at the screen grid when the screen grid is more positive than the anode. [eg like in an output tube with big anode voltage swings]. . Using a suppressor grid [making the tube into a pentode] is one way to make sure secondary emission from the anode does not give the kink. Using beam forming electrodes plus careful alignment of electrode structures is another way. To repeat: "Kinkless Ttetrode" = "Beam power tube". Same thing. No difference. -Martin A. ---------------------------------------------------From [email protected] Mon Feb 12 12:26:14 CST 1996 From: [email protected] (Scott Frankland) Newsgroups: rec.audio.tubes Subject: Re: What is a Kinkless Tetrode? Date: 12 Feb 1996 17:34:18 GMT Distribution: world [email protected] wrote: : I've heard that the "KT" in KT-66, KT-77, and KT-88 stands for : Kinkless Tetrode, and that this is somehow different from a : beam power tube. : Is there any real difference? Who came up with this idea? The kinkless tetrode is a beam power tube [1]. It differs from the ordinary tetrode in the same way that other beam tubes do; i.e., it provides a virtual suppressor [2]. Beam tubes differ from other beam tubes mainly in the manner in which the electron stream is formed; i.e., in the shape and position of the beam formers [3]. The 6L6 was the first beam tube [3]. [1] M.O. Valve Co. Ltd. tube specification, London, England. [2] O.H. Schade, "Beam Power Tubes", *Proc. IRE* Feb. 1938, pp. 162--176. [3] Richard F. Shea, Editor-in Chief, *Amplifier Handbook*, McGraw-Hill, NY, 1966. ~SF~ What is Single Ended What is Single Ended From [email protected] Thu Nov 9 15:55:37 CST 1995 From: [email protected] (Randall Aiken ) Newsgroups: rec.audio.tubes Subject: Re: Please explain "single ended" Date: 9 Nov 1995 02:58:53 GMT X-NETCOM-Date: Wed Nov 08 6:58:53 PM PST 1995 In <[email protected]> [email protected] (Wilhelm Reich) writes: > >What does this mean in amplifier terminology? Thanks Single-ended refers to the output stage topology. The two primary types of output stages for audio are single-ended and push-pull. The main difference is the output transformer. Other differences are explained below. In a push-pull amplifier the power supply is connected to the center-tap of the transformer and a tube is connected to both the upper and lower end of the center-tapped primary. This allows the tubes to conduct on alternate cycles of the input waveform. A push-pull stage can be biased class A, where current flows in both tubes for the entire input cycle, or class AB, where current flows alternately in both halves, but less than a full cycle in each, or class B, where current flows only half the time in each tube. Most designs are biased class AB for best efficiency and power output with minimal crossover distortion (but not necessarily best "tone"). A push-pull stage requires at least two tubes to operate, but can have more connected in parallel with each side, resulting in an amp with four, six, or even eight output tubes for higher-power amps. Other advantages of this circuit are: there is little or no DC current in the output transformer if the tubes are matched and the stage is balanced, since current flows in opposite directions to each tube, allowing a smaller transformer with less iron (translation: cheaper). Also, even order harmonics and distortion products generated in the output stage are cancelled out (translation: good for hi-fi buffs, bad for guitar players!) In addition, power supply hum is cancelled out, allowing less filtering of the supply. This stage generally clips symetrically, resulting in more odd harmonic distortion. One disadvantage is that the DC supply current changes dramatically between off and full signal, requiring heavier filtering to prevent supply "sag", unless that is what you are looking for, as in guitar amplification. A single-ended output stage is always run class A (unless you are talking radio transmitters or a "SEPP" - see below). It's output transformer primary is not center-tapped, having only two connections. One connection goes to the power supply, the other to the plate of the power tube or tubes. Tubes can also be paralleled for more power as in a push-pull stage. This is the type of output stage used in the venerable Fender champ guitar amplifier and countless millions of early radios and tv's. It is making a comeback in high-end vacuum tube audio as a single-ended triode stage, which supposedly is the ultimate in sound reproduction. As inefficient as it is good sounding. Another problem with this type of stage is the transformer must handle a continuous DC current. This results in a physically larger and more costly output transformer, which must be gapped or made of special material such as MPP to prevent saturation of the core. Disadvantages include: no rejection of power supply hum; no rejection of even order harmonics (a great advantage to guitar players!); generally asymetrical limiting on overloads which further emphasizes even order harmonics (which are more pleasing to the ear than odd order harmonics). There is another type of single-ended stage called a "single-ended push-pull" or SEPP. This is similar to a totem-pole MOSFET or non-complementary transistor output stage. One tube is run from a positive supply on its plate and is configured as a cathode follower, the other tube has a negative supply on it's cathode. The transformer (if used) connects to the between the center of the two tubes and ground. Heavy negative feedback is used to assure linearity and minimal crossover distortion. This type of configuration is also used in the OTL or "output-transformerless" tube stages which are scarce as hen's teeth, probably due to the difficulty of matching the tube outputs to low-impedance speakers, and the danger of DC on the speakers. Output impedance of tubes (even in the cathode follower configuration) is high compared to solid-state devices. The heavy negative feedback reduces this output impedance to usuable levels, as well as maintaining the DC output at zero. Hope this answers your questions and didn't put you to sleep! What is a Fetron What is a Fetron From [email protected] Fri Mar 31 23:25:14 CST 1995 From: [email protected] (Tremolux) Newsgroups: alt.guitar.amps Subject: Re: Fetron? (was Black vs. Silverface?) Date: 31 Mar 1995 19:10:59 -0500 Sender: [email protected] Reply-To: [email protected] (Tremolux) George, a "Fetron" was a device originally made by Teledyne Semiconductor back in the 70s. It's basically high-voltage FETs in a 9-pin minature that fits into a 9 pin tube socket. The pinout was such that they'd work in a 12AX7 type application. No, these are not the more modern "hexfet" type of high voltage MOSFETs. I believe they were depletion-mode JFETs. they couldn't take as much voltage as a 12AX7. I believe they, since they're FETS and have more of a pentode type transfer characteristic, provide more gain and less noise than a tube. I actually have a couple of them (somewhere, if I haven't lost them or tossed them out) that I tried in one of my amps way back when. I found the tone to be kind of harsh. regards. What is a Klystron What is a Klystron From [email protected] Sat Apr 8 11:28:17 CDT 1995 From: [email protected] (Tremolux) Newsgroups: alt.guitar.amps Subject: Re: tube sound Date: 7 Apr 1995 16:20:03 -0400 Sender: [email protected] Reply-To: [email protected] (Tremolux) >>And do X-ray machines use tubes? >>->>Tom. >Yes, I think they are called Klystrons. No, X-ray machines use x-ray tubes. They're just simple diodes that run at extremely high voltages, and the electrons slam into the plate with such force that x-rays are produced. Klystrons are microwave amplifier tubes. Klystrons that run at extremely high voltages do produce x-rays, but that is not the intent. I used to work for Litton in San Carlos, Ca. They make the 500 MHz klystrons used in the old BMEWS ballistic missile warning radars, a relic of the cold-war. These things are literally the size of a phone pole, run at about 150,000 volts, use internal liquid cooling (the water is piped around inside the tube to cool it's innards), and the x-rays produced are so hard they have to run the tubes inside a lead-walled booth. Serious stuff. These monsters cost about $100,000 each. Regards. What is a Plexi What is a Plexi From [email protected] Sat Nov 11 16:58:31 CST 2000 From: "Tridders" Newsgroups: alt.guitar.amps Subject: Re: What's a Plexi? Date: Sat, 11 Nov 2000 19:54:32 GMT Xref: geraldo.cc.utexas.edu alt.guitar.amps:285340 Hi, "Plexi" is the nickname given to Marshall amp heads model 1959 that have the clear perspex (a.k.a plexiglass) fascia to the control panel with a gold backing sheet showing through as opposed to the metal plates of the later models. The sound can best be heard on early Free albums. The late great Paul Kossoff had two stacks running on an A/B switch. One stack was on half power, the other was on full steam ahead. A forerunner of the dual channel amp, I guess. Other notable users of the plexi are Angus Young of AC/DC and Eddie Van Halen before he went all "5150". A guitar, a lead, a monster tone. The only problem is that to get that renowned Marshall crunch, the amp has to be run at or near full power. Have you ever stood in front of a Marshall stack on full bore? That's why so many of us old timers are going deef, s s s sonny! ;) cheers, Tridders :o) Thought for the day: Why is it that you can't make other words out of the word "anagram" ? "josiah cantwell" wrote in message news:[email protected]... > What exactly is a Plexi? I gather it's a Marshall tube amp favored by > classic rock artists. > What are the characteristics of the sound (heavy distortion vs. overdrive), > what songs or artists have a typical Plexi sound? How might you try to fake > with with modern effects? > As a classic rock dinosaur myself, I'd appreciate some info about them. > > later, > Si > ---->>>I was going 70 miles an hour and got stopped by a cop who > said, "Do you know the speed limit is 55 miles per hour?" > "Yes, officer, but I wasn't going to be out that long..." > -- Steven Wright > > > Which 4x12 Impedance Which 4x12 Impedance From [email protected] Thu Jul 11 11:17:54 CDT 1996 From: O'Connor Newsgroups: alt.guitar.amps Subject: Re: impedence/sound? Date: Thu, 11 Jul 1996 02:46:04 -0700 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Jeff Vineburg wrote: > > Has anyone noticed any difference between a stock Marshall 16ohm cab, > and one rewired for 4ohms using the correct tap? > The standard series-parallel wiring of most four-by cabinets reduces the ability of the amplifier to exhibit ANY damping over any individual speaker because there is always another speaker "in the way"-- at least >from the amp's perspective. This will produce the traditional "loose" or "floppy" low-end that so many people desire. Wiring all of the speakers in parallel creates a much tighter bass end, as the amp can directly "see" each speaker and dampen the back EMF from each and every driver. There is a recent trend toward this type of sound as guitar players rebel against those pesky bassists that insist on playing in the guitar-range (haha). Every tone has its merit. Kevin Who Made Delco Tubes Who Made Delco Tubes From [email protected] Fri Jun 9 13:37:43 CDT 1995 From: [email protected] (Dr Distortion) Newsgroups: alt.guitar.amps Subject: Re: Tube Questions Date: 9 Jun 1995 16:38:16 GMT GGJaguar ([email protected]) wrote: : GM Delco makes GM O.E.M. car parts and I was wondering if there tubes were : made by RCA or GE or other company. A friend of mine who works for Delco answered that question for me while ago. He said, "Whoever was bidding lowest at the time" :) Who Makes Kendrick Spkrs Who Makes Kendrick Spkrs From [email protected] Mon Feb 17 12:07:39 CST 1997 From: [email protected] (Ted Weber) Newsgroups: alt.guitar.amps Subject: Re: Eminence speaker info sought Date: 17 Feb 1997 16:00:58 GMT >Actually, I think you mean that a number of speaker remarketers are >seeking to have Eminence make them a speaker that sounds like a vintage >Jensen, while as far as I know, only Weber VST(?) is designing and >making them on their own. Yes, that's correct. > I don't know who makes Kendrick) Credence, right down the road from Eminence in Kentucky. > With regards to Weber(sp?), I'm not sure thay make a ceramic >vintage style speaker that can take a full 60-65 watts, but again, all >reports praise them highly. For our high powered 'K' series, we use a generic black basket like everyone else, although beginning next month, we are going to start using our dark green 'hotdog' slotted basket, etc. Ted WeberVST (no relation to G. Weber) Why 16ohm Loads Why 16ohm Loads From [email protected] Mon Dec 28 11:35:53 CST 1998 From: [email protected](Lord Valve) Newsgroups: alt.guitar.amps Subject: Re: 4x12 at 16ohms??? Date: 27 Dec 1998 21:37:07 GMT X-NETCOM-Date: Sun Dec 27 1:37:07 PM PST 1998 Xref: geraldo.cc.utexas.edu alt.guitar.amps:148926 In <[email protected]> [email protected] (jim black) writes: > >I just got a 4x12 cab and I'm wondering why its 16ohms. Wouldn't it >produce better if it was wired at 8ohms instead????Why 16?? > >THANX >BLACKIE Lord Valve Speaketh: First of all, a 16-ohm cabinet *cannot* be rewired to 8 ohms. It can be wired for 4 ohms, or 64 ohms (not useful) but not 8. If by "produce better" you mean it would allow the amp to deliver more wattage, this is only true of solid-state amps...most of which ship with 8- or 4-ohm cabinets anyway. For a tube amp, as long as the output impedance selector is matched to the impedance of the cabinet, the power will be the same at any impedance. Running a tube amp at 16 ohms is advantageous on two counts, however; first, it allows the amp's power to be developed across the entire output transformer secondary winding instead of just a portion of it, as would happen with an 8- or 4ohm load. Second, the higher impedance minimizes the effect of speaker-wire resistance, thus improving power transfer. Lord Valve Visit my website: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NOW ACCEPTING VISA AND MASTERCARD! "It ain't braggin', if ya can do it." - Babe Ruth Why AC on heaters Why AC on heaters From [email protected] Sun Aug 27 18:33:38 CDT 1995 From: [email protected] (TR Simon) Newsgroups: rec.audio.tubes Subject: Re: Heater Voltage AC or DC?? Date: Mon, 28 Aug 1995 01:11:31 GMT [email protected] (SnarfSnout) wrote: >My question: is there a difference/advantage to using AC or DC for for >the heaters. (my shot in the dark... DC is better but in the interst of >simplicity and cost the St 70's use AC????) >Thanks >Dave My understanding in this matter is the main reason that DC (for heater supply) should be avoided, is because of an action similar to electro-plating which causes uneven migration of metal due to the voltage potential across the heater. This in effect causes one end of the heater grow thinner while the other end grows larger. nb. The cathode provides an intgrating function due to its thermal mass. TRS. Why Blackface an Amp Why Blackface an Amp From [email protected] Fri Jun 16 17:17:48 CDT 1995 From: [email protected] (Tremolux) Newsgroups: alt.guitar Subject: Re: Another Twin Reverb Question Date: 16 Jun 1995 16:29:47 -0400 Sender: [email protected] Reply-To: [email protected] (Tremolux) Mark, the reasons I don't like the MV control are as follows: 1. - It adds extra circuit loading prior to the phase inverter, lowering effective preamp gain. 2. - The extra long wires to hook the mofo up add extra distributed capacitiance, noise pickup and stability problems. 3. - MV type distortion on Fenders sounds shitty. It has nothing to do with the phase inverter. Besides, the blackface mod makes the whole damn amp sound better. Regards. Why Bleeder Resistors Why Bleeder Resistors From [email protected] Wed Dec 18 12:45:14 CST 1996 From: [email protected] (Henry Pasternack) Newsgroups: rec.audio.tubes Subject: Re: Tube amp design notes. Date: 18 Dec 1996 16:25:18 GMT Reply-To: [email protected] Andy Moss ([email protected]) wrote: : Henry, you wrote a few messages back about two 10K bleeder resistors in : your tube amplifier. I had mentioned that I found that rather suspect : and you, if I recall, stated it was a generally accepted way of doing : things. : I still don't believe. I would like you to provide some kind of *proof* : to this end. : I think that you may have misunderstood a different design as I can see : no positive benefit to such excessive "bleeding". It reminds me of : "leeching" as being acceptable in medicine years ago. : In short, lay the science on me - not the conjecture..... The output voltage of a choke-input filter is approximately 0.9 times the RMS secondary voltage under load. Unloaded, there is no current flow through the choke, which effectively "disappears". The filter now looks like a capacitor-input, and the output rises to 1.4 times VRMS. To keep the supply under regulation, it is necessary to draw a minimum amount of current from it. Working through the math (which is tedious because you have to do it in the time domain), you end up with a standard equation that states, Imin = VDC / L, where L is given in Henrys. For instance, a 400VDC supply with a 10H choke-input filter requires 40mA of bleed current. In practice, the choke's inductance will rise at low currents, allowing a lower bleed current. There are such things (although they are not common these days) as "swinging chokes" -- chokes designed deliberately to have much higher inductance at low currents than at full load -- intended specifically for choke-input filter applications. I don't have a specific reference handy, but you certainly can find a discussion of all of this in the RDH, the Radio Amateur's Handbook, the RCA Receiving Tube Manual and so on. It's for real, trust me. -Henry -ATTENTION! Reply to [email protected] ([email protected] won't work). Why Cap Value Spread Why Cap Value Spread From [email protected] Thu Jul 29 20:07:07 CDT 1999 From: [email protected] (Ned Carlson) Newsgroups: rec.audio.tubes Subject: Re: Random Question/History of Component Values Date: 29 Jul 1999 19:56:08 -0500 Reply-To: [email protected] Xref: geraldo.cc.utexas.edu rec.audio.tubes:130888 On Tue, 27 Jul 1999 23:45:36 -0700, [email protected] (David A. Anderson) wrote: > >Hi, > >I've been wondering about this for a while, so I've decided to reveal my >ignorance and ask why typical component values have shifted over the last >30 years? > >For example, lot of the older gear I work with has capacitor values of >5uF, 25uF, 50uF, but now, you find capacitors at 4.7uF, 22uF, and 47uF. It maximizes the use of inventory if the values are such that the tolerances (usually 10%, but long time ago 20% was common) just slightly overlap. If you've got 20% tolerance, instead of the old values of .01, .012, 015, .02, .025, .03, .035, .04 and .05, you get .01, .015, .022, .033, and .047. See, right there we've ditched 4 items off the inventory, and forced all the engineers to pick 20% parts whether they like it or not ;-) The Pointy Haired Boss would be proud of us. Ned Carlson Triode Electronics "where da tubes are!" 2225 W Roscoe Chicago, IL, 60618 USA ph 773-871-7459 fax 773-871-7938 12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun http://www.triodeel.com Tube and Tube Amp info on the net... The Big Tube Links Page! Why Care About Phase Why Care About Phase From [email protected] Mon Jun 1 10:43:04 CDT 1998 From: [email protected](Lord Valve) Newsgroups: alt.guitar.amps Subject: Re: speaker wire reversal on re-issue 4x10 bassman Date: 1 Jun 1998 05:52:01 GMT X-NETCOM-Date: Sun May 31 10:52:01 PM PDT 1998 Xref: geraldo.cc.utexas.edu alt.guitar.amps:108085 In <[email protected]> Robert Hinson <[email protected]> writes: > >to aga gurus, in g. weber's first book he has a section on the 4x10 >bassman and says you need to reverse the polarity on the speaker wires >to the current speakers (alnico mojo/eminence) because the signal from >the output section is inverted with respect to the input signal from >your guitar. this part i understand (because of the gain stage type and >arrangement) but why then wouldn't the same be true of any amp using >similar preamp gain structure (marshall, vox, etc.--they all invert the >signal with respect to the input)? he says what you want is the speaker >cone to move forward when signal is applied or when you test the >polarity with a 9v battery. as far as i know, the current alnico >eminence speakers move forward when given the battery test. the only >difference is the orientation (left or right) of the speaker terminals >when compared to the orientation of ceramic magnet speakers. if a >speaker moves forward when given either signal or the polarity test, why >the hell should you reverse the wires? i thought maybe this was just >true with the old jensens which weber says move backward so that is why >one would have to make the wiring change. lord valve, trem, do you guys >have the real scoop on this? maybe there's something about speaker >construction i don't understand or that gerrie left out. thanks rh Lord Valve Speaketh: "Absolute" phasing - whether a single speaker (or an array of speakers) moves inward or outward when presented with a positive-going transient - is really a matter of taste. Some people (I happen to be one of them) can hear this; of those who can, only around half express a preference for one 'phase' over the other. My own take on this is that I don't care much, unless the program material has a lot of kickdrum in the mix and it's LOUD. In that case, I prefer to have the 'absolute' phase be correct. Note that this is really a pretty haphazard process, as (in a large PA system) the signal will pass through many dozens of stages of preamplification, EQ, summing, buffering, etc., and many discrete stages such as the mixer, outboard processing (including compression, EQ, filtering, time-based effects, etc.) electronic crossover, power amplification, and so forth. Some of these stages/devices will invert signal and some won't. If any of these devices use balanced line connections, the 'absolute' phasing will also be at the mercy of the guy who wired the connecting cables. There is really only one way to determine whether an entire system is "in phase," and that requires test equipment. "Relative" phasing is much more important...if you have two speakers wired electrically out-of-phase in the same cabinet, you'll be looking at a pretty drastic drop in low-frequency performance. Having two arrays (like the left and right speaker stacks of a PA system) out of phase with each other is more subtle...the folks in front of the right stack will like what they hear, as will the folks in front of the left stack. The folks in the middle will be listening to some pretty squirrelly cancellation effects, though. As far as your Bassman goes, feel free to try it both ways. You can't hurt anything by running the speakers out of phase with respect to the input signal, so if you actually find that you prefer one phase over the other, go for it. I have a customer who had me put a phase-reverse switch on his Twin; he likes it "in" on some tunes, and "out" on others. Why don't you try it yourself and post the results. Lord Valve Visit my website: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and request a tube catalog. I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes. Good prices, fast service. "I got the chop...I'll never get popped." - Tower of Power Why Change SF Lead Dress Why Change SF Lead Dress From [email protected] Tue Jan 28 09:28:20 CST 1997 From: [email protected] (Karl LaFong) Newsgroups: alt.guitar.amps Subject: Re: Blackface question? Date: Tue, 28 Jan 1997 09:16:50 GMT trekman wrote: > >> >> >>> Note that some retro/blackface aficianados >> actually betray themselves when they suggest certain snips and discards >> for better tone. >> > >What exactly is the difference electronically between the b/f and w/f >amps besides the safer wiring insulation in the w/f's? Please let me >know. >Trekman Be careful calling that plastic Gavitt wire safer..I've seen some very early SF's with the new wire type that had the old style lead dress. Problem is, the plastic "safer" wires' insulation had melted due to the heat and pressure of the eyelet boad (we're talking about the wire under the board) and had shorted underneath the board. Sounds like a great way to get electrocuted. I'm certain that this is what precipitated the funky lead dress in SF amps. I've got a number of '50's and '60's Fenders with the terrible cloth wire that work just fine, thank you. LaFong Why Microphonic Cords Why Microphonic Cords From [email protected] Tue Feb 29 15:30:03 CST 2000 From: "Robert M. Braught" X-Accept-Language: en MIME-Version: 1.0 Newsgroups: alt.guitar.amps Subject: Re: What makes a shit cable? Content-Transfer-Encoding: 7bit Date: Tue, 29 Feb 2000 06:41:10 -0600 Xref: geraldo.cc.utexas.edu alt.guitar.amps:236409 No wankery; as Chris said, one of the noise sources is a 'condenser mike' phenomenom ('space charge'); however, of more significance (my favorite) is the 'triboelectric' effect, which are charges created between a conductor and an insulator due to friction. Think of static electricity, cat hair/rubber balloon, free electron transfer. Historically, graphite can be used as a lubricant/ground path inside the cable for the shield (usually braided, for flexibility/durability) to dissipate the charge/prevent it from occuring in the first place. GeorgeL's is actually a paste/semi-liquid. I've also seen thin carbonized plastic 'tween the braid and the center conductor insulation. Some insulating materials can generate a 'piezoelectric' effect too, this can come up in an old cable that's hardened. Never have figured out how to squirt WD-40 down through my cables to get the tribes to stop being electric..... ;-) Regards, Robert QTS www.Braught.com Why Not Bias By Scope Why Not Bias By Scope From [email protected] Sat Jan 18 21:54:16 CST 1997 From: [email protected] (R.G. Keen) Newsgroups: alt.guitar.amps Subject: Re: `67 DELUXE REVERB BIAS Intructions - PLEASE! Date: 19 Jan 1997 00:10:19 GMT Steve Nielsen ([email protected]) wrote: : On 14 Jan 1997 11:50:32 GMT, [email protected] (Tremolux) wrote: : >Ahhh, the inconsistent, non-repeatable bullshit GT method. Oh well, it's : >your amp. : Hold on now Tremo', ol' buddy! Gimme some reasons. : Why is it inconsistent and non-repeatable and male-bovine-fecal? Well, I'm no Tremolux, but, picking out things from the biasing section of the tube amp faq, I'd say that it's like this: When you bias to give yourself a noticeable notch, you bias it into nearly class B, as the notch is the artifact of the gain changing as one tube turns off. As you increase the overlap to remove this notch, you move it toward class A, and the overlap hides the turn off artifacts by moving them well into the other tube's conduction cycle. The inconsistency and non-repeatability come from the fact that to the human eye, the amount the waveform changes per unit change in bias voltage or current drops dramatically as you move through AB. (If your signal isn't very large, you stay in A - that is, the signal never gets big enough to make one tube turn off.) If you were to plot visual waveform change versus standing current, it changes a lot as you move from B, gets steadily flatter as you move toward A. This is one of those situations where eyeballing is is very difficult to make consistent. It's not because it's impossible, or that you're necessarily inept, it's that the changes get hard to perceive, and people who do this tend to start listening to it to hear differences and drift gradually towards class A, which sounds sweeter. In the tube amp FAQ, I mention that you can do this, and achieve consistent signal quality in biasing, but you need to use a distortion analyzer to measure the quantity that is actually changing (the crossover distortion) and not an oscilloscope where you're trying to make your eyes and brain pick out the distortion in bad circumstances. Why Opto Trem Why Opto Trem From [email protected] Tue Jan 2 14:02:05 CST 1996 From: [email protected] (Joseph Pampel) Newsgroups: rec.audio.tubes Subject: Re: 5881query/new Trem thread Date: 2 Jan 1996 04:59:59 GMT Distribution: world [email protected] (Stephen Delft) wrote: re: Why change from power-stage bias modulating trem to opto-isolators.. > >If you wish, I will start off the thread here. Fitting an opto and >a neon (and saving 1 or 1 1/2 12AX...tubes and a lot of R's and C's) >reduces assembly and component cost. Now....what _else_ were you >considering? I could take a few WAGs at that one.. #1 failing optocouplers will never take out your power tubes.. ;-) #2 optocouplers stop LF/DC pulses from getting through to the outputs/speaker. To see what I mean, check out a Princeton Rvb (or similar) sometime when the trem is on. The speaker moves very slowly in and out on the trem osc wave and if you crank the thing up, I think you'll find it a lot easier to blow the speakers.. Joe From [email protected] Tue Jan 2 14:02:36 CST 1996 From: [email protected] (Stephen Delft) Newsgroups: rec.audio.tubes Subject: Re: 5881query/new Trem th Date: Tue, 2 Jan 1996 09:54:00 GMT Distribution: world (Joseph Pampel replying to Stephen Delft's thread: Fender trem circuit changes.) JP>#1 failing optocouplers will never take out your power tubes.. ;-) JP>#2 optocouplers stop LF/DC pulses from getting through to the JP>outputs/speaker. To see what I mean, check out a Princeton Rvb (or Quite correct on both counts Joe. But this thread flows from comments by Dr Distortion, and I _thought _ he was referring to the _other_ old Fender trem circuit, using a gain-modulated pair of triodes at an early stage in the amp. ( eg Fender Super 6G4 or 6G4A) Why Fender gave up on _that_ one is still a puzzle...it sounds nice, and doesn't take the output stage with it if it goes. I suggested that perhaps someone decided it cost too much. BTW, I have here a NZ made Jansen guitar amp, which bias modulates the output pair of EL84's in the way you were considering, ...but this one applies the trem waveform via a 0.5uF filmcap. So if the trem oscilator dies, it can't do anything bad to the output stage. I will check the speaker for LF wobbles when I get it on the bench for repair. Regards, Stephen Delft. From [email protected] Wed Jan 3 10:40:10 CST 1996 From: [email protected] (Joseph Pampel) Newsgroups: rec.audio.tubes Subject: Re: 5881query/new Trem th Date: 3 Jan 1996 05:10:26 GMT Distribution: world [email protected] (Stephen Delft) wrote: > But this thread flows from >comments by Dr Distortion, and I _thought _ he was referring to the >_other_ old Fender trem circuit, using a gain-modulated pair of triodes >at an early stage in the amp. ( eg Fender Super 6G4 or 6G4A) I thought you were referring to the type in the Vibroverb, Tweed Vibrolux etc. And of course since I wasn't looking at the schematic (trying to be a hero and all.. :-) ) I neglected to notice that .1uF cap that isolates the trem osc from the bias supply in the Vibroverb/Princeton... Oops. So much for my credibility. ;-) I still can't help feeling like it's pretty abusive to swing those power tubes around like that though. That 6Gnn type trem circuit that you meant is one of the nastiest to build in my experience. If you check out the layout diags of those amps (from the Vibrasonic on down) the trem takes up better than 1/2 the eyelet board. With the advent of surf music (and reverb) I think Fender dropped the 6Gnn trem for a bunch of reasons, not the least of which was cost and complexity( as you mentioned), but also so that they could stuff a reverb circuit into their professional combos. Otherwise, it's hard to explain from a mfring standpoint why a mfr would change chassis/faceplates/knobs/etc and retrain for a whole new series of amps after only 2 years of production. The brown chassis did not have much in common with the BF ones.. even the pots have shorter shafts, so changing over to the BF amps was a fairly big expense. They must have really wanted/needed to do it. Just so it's clear I'm not talking completely out of my butt , I have built/restored a bunch of amps of that era using that circuit and they sound great but take at least twice as long to build as anything else out there (short of a univac..) Sounds a lot like a univibe at some settings too. (the trem does..) Regards, Joe P. From [email protected] Thu Jan 4 16:31:24 CST 1996 From: [email protected] (Joseph Pampel) Newsgroups: rec.audio.tubes Subject: Re: 5881query/new Trem th Date: 4 Jan 1996 12:59:42 GMT Distribution: world [email protected] (Stephen Delft) wrote: >Apart from the cost and time to assemble this kind of trem cct. have you >had any problems with getting them to work properly ...different >samples of tube etc. The only thing I've had a problem with is if I use an osc tube with too high a gain: I get loud clicks in the audio. This happens occaisionally with some NOS tubes and most 12AX7WXT's. Going to 12AX7WB's solves the problem. Other than that, the circuit has been no trouble at all. It's a really neat design, with a lot of hidden details. Not a book design, it is clear (upon experimenting with it) that it was designed by that time honored method of tweaking away.. Everything there is there for reason. Gotta admire that. :-) >Any significant differences between the two versions of this trem >(simple versus more complex oscillator/buffer sections) ? Dunno actually. I've only built the more complicated one (the -A circuit. ) But it appears from messing with the circuit a bit that the buffer is there to help maintain the trem wave integrity. They go to great lengths (what, 4 .1uF caps and a .03uF to ground?) to get a nice sine-wave out of the osc, but as you change osc speeds you run into various problems, mainly the weakening of the trem signal though. Keeping the osc output buffered and using that huge (10-Meg RA!) intensity pot keeps the trem signal strength pretty constant over the speed range. Another advantage of the buffered circuit is that it also incorporates the cathodyne phase inverter to obtain the 2 out of phase trem signals. This is almost certainly a better balanced circuit than the paraphase PI used in the earlier examples, especially in the SLF region of interest in this case (3-12Hz or so). Surprisingly, the trem signals do not cancel in the mixer tube though. You get a really funny looking artifact at the mixer output.. part of the charm of this circuit.. :-) (and why they use a really small coupling cap to the output stage.. IMHO) Nice to hear from you! Joe P. Why Select Highest Z Tap Why Select Highest Z Tap From [email protected] Sun Apr 16 00:01:24 CDT 2000 From: Lord Valve Newsgroups: alt.guitar.amps Subject: Re: Audible difference in 4 / 8 / 16 ohms? Date: Sun, 02 Apr 2000 22:40:12 -0600 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Server-Date: 3 Apr 2000 04:33:36 GMT Xref: geraldo.cc.utexas.edu alt.guitar.amps:243148 Richard wrote: > I was talking to friend about amps today, and the topic came up about > whether using the 4 or 8 ohm output of a tube amp offering both makes a > differences in amp sound. > > I didn't know, and he said he just always used the 8 ohm output. > > What's the scoop, please? > > -> Disclaimer: These are simply some of my personal opinions. > ObURL: http://home.earthlink.net/~huddler > > "Cognitive dissonance is your best friend." Lord Valve Speaketh: Well, here's my take on it: I always run the highest impedance the amp is capable of driving. The main reason for doing so is that the power will be transferred to the load via the *entire* output transformer secondary winding, rather than just a portion of it. This allows for even heat distribution in the winding, with a consequent increase in reliability. The damping factor will be marginally better at the highest impedance, which may result in slightly better low-frequency performance. In addition, the resistance of the speaker cable (and any internal cabinet wiring) is much smaller when considered as a percentage of the total load impedance; this means that less power is dissipated by the cable as heat. If, for instance, the speaker cable and the internal cabinet wiring added up to 1 ohm (it wouldn't, but round numbers will make this a lot easier to understand), the total load seen by the amplifier when driving a 16-ohm rated cabinet would equal 17 ohms. This means 1/17th of the amp's output power will be turned into heat within the cabling. Using the same cabling and internal wiring, but this time with a 4-ohm cabinet, the total load seen by the amplifier would be 5 ohms. In this case, 1/5th of the amp's output power is now wasted as heat...considerably more. (Of course, this is a very simplistic model. Factors such as impedance variations in the speaker voice-coils due to applied frequency, the complexities of a load which is partially resistive and partially reactive, etc., have been ignored in this example.) Is there an audible difference? Probably, but it would be *very* hard to quantify; the fact that an amp sounds one way driving a 4-ohm cabinet and another way when driving a 16-ohm box would be more affected by the difference in the speakers themselves than by anything else. No two speakers are ever exactly the same, and it would be impossible to find two cabinets that were *identical* in every respect save the impedance...and that is exactly what you'd need to make the comparison. Lord Valve VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NBS Electronics, 230 South Broadway, Denver, CO 80209-1510 Phone orders/tech support after 1:00 PM Denver time at 303-778-1156 NOW ACCEPTING VISA AND MASTERCARD CHAT WITH LORD VALVE: Log onto any DALnet server and join channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. "I got the chop...I'll never get popped." - Tower of Power From [email protected] Sun Apr 16 00:02:20 CDT 2000 From: Lord Valve Newsgroups: alt.guitar.amps Subject: Re: Audible difference in 4 / 8 / 16 ohms? Date: Mon, 03 Apr 2000 11:50:13 -0600 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Server-Date: 3 Apr 2000 17:44:50 GMT Xref: geraldo.cc.utexas.edu alt.guitar.amps:243237 Cybernalt wrote: > " I always run the highest impedance the amp is capable of driving ... This > allows for even heat distribution ... [and] increase in reliability. The > damping factor will be marginally better ... which may result in slightly > better low-frequency performance" > > LV: Are you assuming multiple taps on the OT? Do these benefits apply if it > has only an 8 ohm tap, and you run it at 16? Lord Valve Speaketh: Yes, I'm assuming a multiply-tapped OPT. No, there are *no* benefits to running an incorrect impedance; in fact, loading an 8-ohm output with a 16-ohm speaker can lead to fried tube sockets (or worse) from flyback. A tube amp can only deliver its rated output into the correct impedance; any other load results in less power. Lord Valve VISIT MY WEBSITE: http://www.freeyellow.com/members2/lord-valve/ Good tube FAQ for newbies. Click the e-mail link and join my SPAM LIST; just put "SPAM ME" in the header and I'll sign you up. (If you only want a set of e-mail catalogs, put "CATS ONLY" in the header.) I specialize in top quality HAND-SELECTED NOS and current-production vacuum tubes for guitar and bass amps. Good prices, fast service. TONS of gear and parts in stock...let's DEAL! NBS Electronics, 230 South Broadway, Denver, CO 80209-1510 Phone orders/tech support after 1:00 PM Denver time at 303-778-1156 NOW ACCEPTING VISA AND MASTERCARD CHAT WITH LORD VALVE: Log onto any DALnet server and join channel #CONELRAD. Look for me there most any night after 11:00 PM Denver (Mountain) time. Guitar-amp questions and what-have-you are welcome. "I'm not an asshole, but I *play* one on the Internet." - Lord Valve Why Sprague Caps Why Sprague Caps From [email protected] Sun Jan 7 09:35:39 CST 1996 From: [email protected] (David Taylor) Newsgroups: alt.guitar.amps Subject: Re: SPRAGUE CAPS! Date: 7 Jan 1996 06:33:44 GMT Mime-Version: 1.0 In article <[email protected]>, [email protected] says... > >I have heard that the caps from Sprague are similar to >those in old Fender amps... is it true? Yes. Especially the axial electrolytics in Sprague's "Atom" series. >In what way were these so special? A lot of people feel it's because they are large, similar in size to the original cardboard Mallory caps found in tweed and blackface Fenders, but the fact is they're just good, consistent quality caps with a fairly low failure rate. Perhaps this consistency and quality has something to do with their size, but the important thing is they maintain their capacitance where the cheaper, smaller ones don't. Why Use Grid Stoppers Why Use Grid Stoppers From [email protected] Sun Jan 26 23:51:42 CST 1997 From: [email protected] (Karl LaFong) Newsgroups: alt.guitar.amps Subject: Re: ' 62 Concert mods Date: Mon, 27 Jan 1997 00:20:03 GMT mgarvi >I suppose Weber would remove the 1500 ohm grid stoppers on the power >tubes, too (No, don't do it!). They are there for much the same >reason as the 68k. There is already 'series resistance' in the driver >circuit, in the form of the 12at7's plate resistance in parallel with >the 82k or 100k load resistors...so why put in a little 1500 ohm >resistor? To get some resistance *close to the output tube*! I think >Fender's location of the 68k input resistor was a manufacturing >convenience, as the same holds true for its location (as you have >pointed out). Tale from the trenches: On my Bassman amps, we were noticing a profound :pop: when the standby switch was turned on. Since we were following the 5F6-A circuit, we were building them w/o grid stoppers. Desipte the efforts of my very able techs, we were unable to locate the source of this momentary parasitic ocsillation. Then one day an amp displayed a wildly ocsillating 6L6. We tried everything but couldn't figgure out why this amp was so unstable. Then like the proverbial 16 ton weight, it hit us. The amps had no grid stoppers. We put 'em on, and voila! no ocsillations! We also noticed that the standby :pop; was gone too. After reflecting on this, we felt like fools for not thinking of this right from the get-go, but it goes to show ya how important the lil buggers are in preventing instability. Les(Plopa) my head tech, was particularly embarrassed for not thinking of it sooner. Evidently the 1500ohm grid stoppers knock the Q out of whack in what is in essense an tuned circuit going to the power tube grids. MBaier >Incidentally, for anyone interested, pentodes are not as prone to >treble loss due to grid capacitance (as compared to triodes), due >to diminished Miller effect. >MGarvin Why Use Standby Why Use Standby From [email protected] Wed Oct 18 12:32:54 CDT 1995 From: [email protected] (Mark Garvin) Newsgroups: rec.audio.tubes Subject: Another reason to use STANDBY switch Date: 18 Oct 1995 12:33:07 -0400 I just posted this to a.g.amps but realized it may be relevant here as well. Pardon the dual post. ===================================================================== Cathode stripping occurs when current gets pulled thru the tube before the tube is warmed up. Most techs know this. But consider what else happens. Tubes that are not warmed up will draw appreciably less current. This means that there will be very little voltage drop across resistors in the power supply. And that means that the full unloaded B+ voltage will be applied to the poor low-rated electrolytics in your preamp section. In other words, if the main B+ is 450v and your preamp supply is 320v, the preamp will usually have electro's rated at 350v or so. If the tubes aren't warmed up when the standby is flipped, the preamp will get a shot of 450v! How about that for motivation? Regards, Mark Garvin Why rectifier is separate Why rectifier is separate From [email protected] Wed Sep 17 13:47:23 CDT 1997 From: [email protected] (Duncan Munro) Newsgroups: alt.guitar.amps Subject: Re: Rectifiers? Confused Date: Wed, 17 Sep 1997 18:23:18 GMT Reply-To: [email protected] X-NNTP-Posting-Host: muffy.demon.co.uk [158.152.92.172] Xref: geraldo.cc.utexas.edu alt.guitar.amps:64059 On 17 Sep 1997 07:23:18 GMT, [email protected] (Your Name) wrote: > Can one retrofit a tube rectifier to an amp if it does not have a spare 5 >separate filament winding ? Could you use an indirectly heated rectifier >tube and run it off the normal 6 volt filament suooly ? has anybody done >this ? would a better method be to use a small separate filament >transformer to the chasis ? How do they make a dual rectifier setup? Hi Steve, Tube rectifiers are not normally run from the 6v filament supply, as this would put the whole filament supply at B+ potential. Normal tubes in a guitar amp allow a maximum filament to cathode potential of 100V to 200V, so this would rule this one out.... Maybe a seperate transformer would be a better idea??? HTH, Duncan -Duncan Munro Check out http://www.muffy.demon.co.uk/ for Homebrew guitar amps and SPICE models