Hi JP: at the risk of putting another info source in play, I recently (finally?) bought Dave Hunter's 'The Guitar Amp Handbook' (Backbeat Books, 2005, 240 pages, paperback). The book is a well integrated and blended (schematics and pictures) approach to the general subject of why amps sound like they do. There is some general discussion of ampology, characteristic sound, and underlying electronics expressed nicely as 'worked examples'.
Starting w/ early Fenders and finishing w/ Dr Zs, Mesas, and Soldanos, Hunter - having laid out why amps sound hot, crunchy, distorted, clean, woofy, or many other 'sound flavors', takes as many as 12 circuits, integrating schematics and pics, and allows the reader to follow along; paraphrasing: "...people like these because of the early breakup..." and then proceeds to tell you why they break up early. Further paraphrasing: '...wanna be Ted Nugent?...here's what it takes to produce that sound..." but with both schematics and pics so you can 'see'; either diagrammatically if that works or just tracing the circuit in the pics: 'signal comes in here, goes there ...'
Excellent discussion of 'Class A' amps; why they sound the way they do and Push/Pull amps and how they are different without beating the electronics to death. The book expresses these disinctions by kind of putting it back on the player: what kind of sound do you want to make? Blues, rock-a-billy, C&W, classic, 'Guitar-God', and so on, and, under what circumstances are you going to make it? Recorded w/ your pals, small venue, or before 25,000 screaming fans nicely making the point that, as with instruments, there is no amp that will do everything and that trade-offs are inevitable.
He leaves it at if you want vintage tone at high volume, get a vintage amp and use a PA. If you want/need a 'wall of music', go get a whopper Marshall stack but don't kid yourself about getting the them both in the same place. FYI, he didn't reference any 'classic' Gibson / epiphone amps directly :evil: but the venerable GA19 RVT rated a passing wave :wink: .
For my part, I liked Hunter's discussion of tweaking the older, smaller Class A amps and early cathode-biased Push/Pulls (sorry, didn't mean to start techno-breakdancing on you) but his point is that older v. newer and 'Class A-sounding' v. 'Clean-sounding' amps generally break nicely along the 'bias' fault line; that Class A amps and smallish-output push / pull amps (typically twin 6V6) that are cathode-biased sound like Class A amps (even though technically they are not) and 'fixed bias' amps - fitted with bias pots - tend to be louder and cleaner.
Finally a very fine discussion along the lines of where Kap'n was trying to take us here:
LTG Thread Voicing Amps talking about cathode caps in the pre-amp, bias, and negative feedback. Hunter generally indicates that with just these 3 principles, anything from Kalamazoos, Premiers, Champs, Silvertones, or any other smaller, 'browner' amp can be made looser, cleaner, gainier, grittier and so on providing a chance to implement some of these ideas w/o carving up museum pieces or scratch-building. cj