Care and Feeding of Vacuum Tubes (Valves)

On Mar 14, 2013, at 8:59 PM, Chuck Guzis <cclist at sydex.com> wrote: Well, you can get a lot more gain out of even a cheap transistor than you can from a good preamp tube. The feedback comes free, at the price of some stability/ flatness of response headaches. Of course, there's also the fact that when transistors distort, they sound subjectively "nastier" than tubes do, so it makes a lot of sense to use lots of feedback. You can also approach the parts-per-million THD with a solid-state amp, something you'd never even get close to with a tube amplifier (not an audio one, anyway). In a guitar amp, common practice is to maximize gain largely by removing the feedback path (it also lets you use much simpler transformers for the speaker, which is great news for manufacturers). Of course, most guitar amp speakers have 3db points not much further from 5 KHz and 200 Hz, so fidelity isn't the main concern. Most of the higher-power ones are class AB, but there are a few famous class A amp models. I don't know why anyone would run in class A for more power, since it's generally a lot less power efficient, but you do get rid of some crossover distortion (in exchange for some odd-harmonic clipping distortion). - Dave