Tube Bass amp circuits - The Amp Garage Oct 04, 2010A somewhat simple circuit so that I can experiment with some tweaking of bass amp circuits. I found this schematic of a tube amp that was supposedly a decent Bass circuit. I have to admit the wiring between the Tone stack and V4 output leaves me scratching my head a little. Guitar Amplifier Schematics - Guitar Nucleus Guitar Amp Schematics. WARNING - If you are not a qualified technician please do not attempt any repair you are not confident with. Amplifiers (especially tube amps) contain high voltages that can kill ! Even when unplugged the capacitors can still contain a substantial charge and must be discharged before attempting any work.