The Rangemaster is kind of a Treble Booster, which at maximum volume on guitar loads the guitar pickup with it's input capacity and functions more like a midrange booster. Properly set up with the gain of the following amp, you get a metal clean treble sound on lower volumes with little distorion and a mid-power fully distorted sound in maximum volume on guitar. This is one of Rory's specialities in guitar sound, he didn't use a footswitch to get distortion. The original Rangemaster works best with Fender Guitars and VOX or Marshall amps, but the germanium transistor was very noisy.
This is not the original Rangemaster circuit, but has same effect. My recommandation for transistor is the low noise BC109C. The bias schould be corrected by variing R6 to get the voltage at collector9V * (10+5) / (10+10+5) = 5.4V.
Settings: VOLUME: 8 (R3=R4=125k), TONE: 10 (R2=250k)
Result: The resonace of the pick up is at 10 kHz.
Settings: VOLUME: 8 (R3=R4=125k), TONE: 0 (R2=0)
Result: The resonace frequency is lowererd to around 400 Hz.
Settings: VOLUME: 10 (R3=0,R4=250k), TONE= 10 (R2=250k)
Result: The resonace frequency is lowered to 1.2 kHz.
Comment: the resonance frequency can be altered by changing of C3