Here are some excerpts from Brach’s response:
It is true that (most of the time) transistors, technically speaking, have much lower distortion characteristics than tubes, but from an audio perspective having less distortion doesn’t necessarily sound better….the type of distortion is what matters. You’ve probably heard that tubes produce even order harmonics, which when added up make octaves of the original signal, and when applied to audio give a much richer, fuller sound. Transistors have a tendency to impart odd order harmonics which add up to be square waves, and when applied to audio sound harsh and buzzy.
So everyone agrees that tubes “sound” better than transistors for most practical audio applications. But why acoustic type tube amps aren’t being produced has nothing to do with sound quality, it is mostly of a practical nature, coupled with demand. There’s probably not enough potential customers in the world who would be willing to lug a very expensive twin reverb sized amp to their gigs and practices just for acoustic guitar.
But just because this might be unfeasible as a business idea (mass produced), it does intrigue me as a hobbyist. In fact, a couple of years ago in my spare time, i was working on a tube driven preamp for use with bass or acoustic guitar. I was designing it just for my use with no intention to market it. i was planning on using it with a PA power amp. I personally prefer acoustic instruments to be run through tube preamps into solid state power amps. To me, it’s the best of both worlds because the tube preamp helps impart some nice harmonic overtones while the solid state power amp has so much head room that you never hear the ugly sounding harmonic distortion.