The EHX Germanium OD offers 60s overdrive tones using a combination of germanium and silicon transistors (all PNP). All 3 pots control the voltage is some way. The Bias pot controls the amount of voltage that reaches the Gain control, which in turn controls the remaining voltage that gets to the germanium transistor. The Volts control acts like a sag control on the overall voltage the circuit is running at, so you can emulate a dying battery. I’ve laid this out for on board pots mounted from the solder-side of the board using right angle PCB mount pots.
