A guitar amp is a very special animal. They’re meant to create a sound of their own not reproduce a sound that they’re fed. Electric guitars can’t make sound by themselves. The amp (a guitar amp is usually a combination of amplifier electronics with a speaker) is part of the “instrument�. And electric guitar without an amp is like a carburetor without an engine.
To create their own sound guitar amps are deliberately designed to operate the tubes in a highly nonlinear range of their transfer function. This creates an extremely complex relationship between the input and output.
An audio amp’s job is to make an exact reproduction (only larger) of whatever it’s fed. It shouldn’t change the signal in any way, shape or form other than to make it powerful enough to drive a loudspeaker. Audio amps’ electronic devices are utilized in their most highly linear operation ranges.
If transistors and tubes exhibited perfectly linear operation the output of either type of amp would be identical. The reality is that neither is perfect, some of either can be absolutely awful and some of either can be pretty darn good.
Transistors and tubes are also fundamentally different in their transfer characteristics. (And, to add even more confusion, bipolar transistors are fundamentally different form FET transistors.) So it’s a scientific fact that the outputs of various amplifiers are different from one another, what’s hotly debated is how/if those differences are audible.
The solid-state camp argues that the tube guys just like additional distortion, the bottleheads counter that silicon’s specific distortion products are nasty and unnatural. Both sides can produce excellent examples of their art. Neither has a clear winner in every circumstance.
I like to think of it much like FWD, RWD, AWD cars. There are talented designers that make great examples of each genre. Each can have advantages under certain circumstances. All can be a ton of fun to drive.
PC.