a few years back i made a tube preamp "stomp box" using "subminiature" tubes, with plate voltages at 24V. it actually worked quite well. at low gains, the tube characteristic added just a barely audible even harmonic distortion, cranked up to full gain gave a nice smooth tube fuzz..... i don't remember the tube type off the top of my head, but i have a bunch of them at home.... basically a submini dual triode similar to a 12AT7, or 12AU7 (not as much gain as a 12AX7). since they were military tubes, they're extremely shock resistant.....
if you put your "component ladder" and switches (i also think relays and a mute circuit is the right way to go) on the cold side of a plate coupling cap, and keep DC out of the mix, you won't have to worry about thumps. also, another good place to do this is in an amp with an effects loop, where it's all line level (max 1.5Vrms) signals anyway, or parallel to the reverb circuit.