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potentiometer with a fourth terminal??? - Printable Version

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potentiometer with a fourth terminal??? - bridkarl - 10-15-2025

This is a replacement volume pot I plan to install. The original Philco pot has four terminals - three at the top and another at the bottom. What is the bottom terminal doing? Where would that resistor be attached if there isn't a fourth terminal?

RE: potentiometer with a fourth terminal??? - RodB - 10-15-2025

The 4th terminal is a tap in the pot. Your schematic should show it, it's typically at 50k and is used to improve the bass at low audio volume. Without the tap you've redesigned the circuit. Maybe someone else can chime in with a suggestion for running without it. It may be more work than it's worth but you might want to find a radio circuit that has no tap but has bass compensation.

RE: potentiometer with a fourth terminal??? - bridkarl - 10-15-2025

This is a 2 meg pot with a 1 meg tap. Philco part number 33-5275. I have a parts unit but long term maybe I can find a source

RE: potentiometer with a fourth terminal??? - RodB - 10-15-2025

I just happened to have a Philco 2meg pot with a 1meg tap, shaft is 1-7/16 long from face of pot. Flat on shaft is 2/3 (Philco).

RE: potentiometer with a fourth terminal??? - radiorich - 10-15-2025

Hello Bridkari,
I know just the person who can help you Mark Oppat He sells radio parts also has a huge inventory of Volume controls and replacement parts to make you control .
Here is Mark's website 
old radio parts
Sincerely Richard

RE: potentiometer with a fourth terminal??? - bridkarl - 10-15-2025

RodB set me up with a part, but I’ll write Mark as I’ll probably need another one. Thanks.