Re: Bass multi effects processor
There's a ton of amps and pedals running tubes in the circuit now, but tubes only start behaving badly, AKA like tubes, when you're running them at proper plate voltages. It's all hot and crazy and the saturation/compression/warmth/distortion is all beautiful and harmonic. You can ALSO run a tube a low voltages, known as starved-plate. You can power a 12ax7 tube with 12v, no problem, but the circuit is more or less operating as a slightly off tolerance transistor and not coloring the circuit particularly much. All of the tubeyness comes from saturation of the tube at high voltage.
There's a system that some mic pres use, like ART, which are an array of voltage doubling transistors or diodes that get the tube running nice and hot, but it's seldom used.