Gibson/Fender Amp Comparison
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Say what?
In dealing with tube amps, one of the questions that gets asked a lot is "what is the Belchfire Quintessential amp like? Will it sound like a FenderMarshallVox Bassman JMP AC30?"And of course the answer varies from amp to amp, and from individual to induhvidual answering the question.
One brand I hear this sort of question about a lot is Gibson. Since I'm a big Kalamazoo fan and Kalamazoo was a Gibson line, I pay a bit more attention to Gibsons than to some of the other, less common brands. In researching the Kalamazoo line I noticed that the Kalamazoo Model One used the same circuit as a Champ, with slightly different values (including different value tubes 8^). I also discovered that at least one version of the Gibson GA-5 Skylark used exactly the same circuit as the Model One. Further investigation brought to light the fact that quite a few Gibson amps were extremely close, circuit-wise, to various Fenders. (Others were unlike anything else anyone built!)
I'm not going to draw any conclusion as to who copied whom. In the early days of vacuum tube electronics, almost everyone started from the same pages - pages from a handful of tube reference books, data books and manuals. Most circuits at least started out as copies of someone else's circuits; then the new circuit was "tweaked" to the new designer's specs, or simply to not be an exact clone of the original. (An awful lot of electronics and software is still handled this way!)
Cavenewts
Or more commonly, "caveats". I am by no means a Gibson amp expert, although I'm slowly getting to know as many as possible. I am somewhat of a relative expert on Kalamazoos, by virtue of interest and the fact that so few other people today have much experience with them. But with Gibsons, I know only what I have read and seen. The following comparison table is based primarily on the time I have spent poring over schematics and old, Gibson marketing literature, the few Gibsons I have been able to work on, and information gathered from people I know who have a lot of Gibsons. I have put a good bit of time into this, but it's by no means an exhaustive comparison, and anyone with much experience knows that tube amp sound is more than simply the components connected as defined by a schematic. But the same experience also shows that with careful tweaking and tube selection, and the right speakers (and sometimes cabinet), any two amps based on the same circuit can usually be made to sound very similar.Furthermore, Gibson felt free to make rather drastic changes with some models, with circuitry, tube complements and even model names. So there may well be models of the same name which do not correspond as noted below. The best example I'm aware of is the GA-5, which came in at least three variants under the name "Skylark" (one 6BQ5, two 6AQ5s, two 6BQ5s), and another version named the "Les Paul, Jr" (6V6, like a 5C1 Champ). A minor example is the GA-70 which was marketed as "Country and Western" and as "Country Western". Furthermore, Gibson used letters after the model number to differentiate whether an amp was plain (no letter), had temolo (T), had reverb (RV), had tremolo and reverb (RVT) or had vibrato (V). Sometimes the enhanced models were the same as their corresponding base models, but other times there was little similarity beyond the model number.
Finally, Gibson changed preamp tubes more frequently than Fender, using the 6EU7 instead of the 12AX7 in some amps, but switching at will. But they also were making great use of the 6BQ5 before it was very common in guitar amps.
So take the data below with a grain of salt. Please feel free to send observations, corrections), qualifications, quotations, additions and any other -ations and -tions (as well as chocolate, which is always appropriate).
Gibson Model Fender Equivalent Main Differences, Notes GA-5 Skylark
single-ended 6BQ55F1 Champ GA-5 has tone control, uses 6BQ5 and 6X4, has no NFB loop GA-5 Skylark
or GA-5 Les Paul Junior
single-ended 6V65E1 Champ GA-5 uses only resistors in PS filter, no choke GA-5T Skylark
push-pull 6AQ56G2 Princeton Gibson tremolo oscillator circuit, uncommon output tubes GA-6
push-pull 6V6s5C3 Tweed Deluxe almost a clone, except uses 9 pin preamp and PI tubes, and some component value variations GA-6 Lancer
push-pull 6V6s5D3/5E3 Tweed Deluxe cross between the two Fender circuits GA-8 Gibsonette
two 6V6s in parallel5E1 Champ, 5F2-A Princeton GA-8 has no NFB loop, uses one less PS resistor GA-8T Gibsonette
push-pull 6BM8s6G2 Princeton Gibson tremolo oscillator circuit, uncommon output tubes GA-8, GA-8T Discoverer
push-pull 6BQ5s??? ??? GA-9
two 6V6s in parallel5E1 Champ, 5F2-A Princeton tweed Deluxe tone cntrol, NFB returns to 6V6 grids, input resistors larger GA-14 Titan
push-pull 6V6s5D3/5E3 Tweed Deluxe cross between the two Fender circuits BA-15RV (bass amp!)
push-pull 6V6spre-5F6 Bassman BA-15RV has only a single rectifier tube, plus reverb. may have been a GA-15RVT Explorer less tremolo GA-15RVT Explorer
push-pull 6BQ5s??? modified GA-16T, plus Bass and Treble controls, plus reverb, with transformer PI GA-16T Viscount
push-pull 6V6s6G2 Princeton Viscount has basic Gibson tremolo oscillator GA-17RVT Scout
push-pull 6AQ5sNONE Sort of a GA-30RVT with 6AQ5s GA-18T Explorer
push-pull 6BQ5s6G2 Princeton same as GA-16T, plus Bass and Treble controls and a monitor out jack GA-19RVT Falcon
push-pull 6V6s6G2 Princeton GA-18T with reverb and 6V6s GA-20RVT Minuteman
push-pull 6BQ5sAA165 Pro Reverb (almost) Gibson tremolo oscillator, transformer phase inverter GA-25RVT Hawk
push-pull 6BQ5s6G2 Princeton with Reverb plain tone control plus fixed midrange control GA-30 Invader
GA-30RV Invader
push-pull 6V6s5E5-A Pro or
5E4-A SuperGA-30s have no cathode follower, just Tone control GA-30RVT Invader
push-pull 7591s!AA1069 Pro Reverb GA-30RVT has Fenderish tremolo oscillator! GA-35RVT Lancer
push-pull 7591s!AA165 Pro Reverb (almost) same as GA-20RVT GA-40 Les Paul
push-pull 6V6s(6SJ7 pentode preamp) Bassman (sort of) GA-40 has tremolo, push-pull output, some have no tone control GA-55RVT Saturn
push-pull 6L6s6G8 Twin plus reverb GA-60 Hercules
push-pull 7591s??? ??? GA-70 Country Western
push-pull 5881s5F4 Super GA-70 has mod. DR-type tone stack GA-75 Recording
push-pull 6L6s6G8 Twin no tremolo GA-77 Vanguard
push-pull 5881s5E7 Bandmaster or 5E4 Super no real equivalent, but these are closest GA-79RVT Multi-Purpose
stereo, push-pull 6BQ5s each sideAA964 Princeton Reverb (with 2 amps in 1 cab) no real equivalent; this is closest approximation. unique, angled speaker cab for channel separation, reverb and tremolo only on channel one GA-80 Vari-Tone
push-pull 6L6GBsNONE two channels, one with push-button tone settings. used 5879s in second preamp stages GA-83S Stereo-Vib
stereo, push-pull 6BQ5s each side??? ??? GA-86 Ensemble
push-pull 6BQ5sNONE single channel version of GA-79RVT, but with a 6V6 driving the middle leg of the output transformer! Tres bizarre. GA-88S Stereo-Twin
stereo, push-pull 6BQ5s each sideNONE similar to GA-79RVT, but no reverb or tremolo, with separate head and two speaker cabs GA-100 Bass
push-pull 6L6GCsNONE funky design using cathodyne inverter to drive pentodes which drive the 6L6GCs, plus tube compression using two 6FM8s (triode, dual diode)
Terminology:
Choke: A coil used to remove ripple or some types of AC from a circuit DR: Deluxe Reverb NFB: Negative FeedBack PS: Power Supply
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Last updated: 23 August 2005Copyright Y2K,2004 Miles O'Neal, Austin, TX. All rights reserved. Miles O'Neal <roadkills.r.us@XYZZY.gmail.com> [remove the "XYZZY." to make things work!] c/o RNN / 1705 Oak Forest Dr / Round Rock, TX / 78681-1514
Data from Aspen Pittman's The Tube Amp Book, 4.1th Edition, Gerald Weber's A Desktop reference of Hip Vintage Guitar Amps, personal knowledge and schematics, and the most comprehensive Gibson amp web site I'm aware of, at http://hem.passagen.se/ekabjan/GibsonAmps.htm .