Drange Control determines how much Soft Knee Clipping is applied
Drive Control adjusts the Overdrive gain (before the Germanium diode circuitry)
Germanium Diode switches: Plus (+) applies clipping to the positive portion of overdrive. Minus (-) applies clipping to the negative portion of overdrive
Output knob adjusts the final Output Gain (0db to +3dBu); Tone knob adjusts final High Frequency