[skyebook]

For a PA system? I'm pretty sure all of that is using transistors now.

For a guitar amp, I hear you (though I also think the quality of things like guitar rig in the last few years have started to sound pretty believable)

[Jugurtha]

I meant both. I've talked to guitarists/electronics engineers who design amps for their guitars, but they're still in use, I think. If my memory serves me well, Marshall still uses them.