yeah, i've read the wiki page. i was wondering if i could get a description of their sound from the fine folks here (i find it very interesting to hear people's terminology when they describe the sound of an amp). or even some clips if they are good ones.
It's hard to explain....but imagine a hot-rodded Fender Twin.....excellent note clarity but with a gorgeous smoky crunch.
It's a distinctive sound, and a good one. But you can get close with a good tube amp, and there are a lot of them, and a really good pedal....the ones I mentioned above for example.
The main thing is that a tube amp sounds much different to a solid state.....and not just because it sounds 'warmer' as many people believe (though they do of course). It runs deeper than that.
If you look at the harmonic distortion of tubes on a spectrum analyzer, you will see a very strong 2nd order harmonic along with the predominant 3rd order harmonic, and more of the rest of the even and odd order harmonics than you will see in a solid state device. Solid state devices like transistors, FETs, MOSFETs and opamps have primarily third, fifth and seventh order harmonic distortion and very little of the rest of the harmonics. Musically speaking, the second is an octave above the fundamental and is almost inaudible yet it adds body to the sound, making it fuller.
essentially, this means that, first, the tube generally sounds "warmer" to the listener's ears. This is due to higher levels of harmonic distortion in tubes than in solid state devices and I think that also accounts for some of the reasons why some guitar players dislike distortion pedals - they can hear that difference.
secondly, power tubes also have higher levels of inherent distortion when pushed to their limits than preamp tubes do, and EL34s have more than 6L6s do for example. For these reasons, I guess it just sounds better when the clipping is occuring at the output stage than it does in the preamp stage because the original signal hasn't been pummeled to death in the preamp stage. You can get a more dynamic sound because of this. NB: Al though EL34's have higher levels of inherent disstorion, in relaity, that breakup often has as much to do with the circuit design (voltages, mainly) as the tubes' inherent tendencies....just the way amp manufacturers gerenally use them...they see that as the right way to do things. Call it psychoacoustics if you like!
I'm not sure of everything that's going on in an amp that creates distortion in the preamp section (as most of them do), but they are basically clipping the heck out of the signal and then sending that to the power amp section. There's basically two ways to control the amount of clipping - in the preamp section and/or in the power amp section. The type of amp also is important. A single ended Class A amp will generally distort much more easily than a Class AB will.
That being said, I have also heard some solid state amps that I feel have a killer crunch to them. One example would be the Lab Series L5 - Ty Tabor uses one to great effect on the early King's X albums.
So set a good valve amp to the point of break up, and push it over the edge with an OD pedal...fine tuning is done with your volume and tone controls on your guitar (and I use RS electronics upgrade kits on all my guitars....you won't believe the difference til you've tried it....imagine; vol and tone controls that work smoothly and taper off evenly without interering with each other, even at low settings)....this should give you a good tone.