[NV3G]

The Sears 1708 radio is a superheterodyne receiver with a 175 KC intermediate frequency. The 500K potentiometer is between the ( 75 ) tube detector and audio grid. The schematic can be found at

http://www.nostalgiaair.org

I do not know what the taper of the potentiometer or rheostat is. The rheostat is the variable cathode resistor in the RF amplifier ( 78 ) cathode and the first Oscillator/Detector tube ( 6A7 ). I have not seen this design before where your increasing the audio volume and decreasing the cathode resistor at the same time.

Thanks for your interest.

nv3g
Oscar -