Capacitor Outside Foil Identification Using an Audio Signal Generator & Signal Tracer

An alternate method for identifying the outside foil of a modern day capacitor using an Audio Signal Generator and Signal Tracer in lieu of your fingers (50/60 Hz by induction) and an O-Scope.

Correct capacitor polarity can help reduce noise, hum (e.g., in close proximity to the heater/filament string, AC line cord, etc.) w/ the foil side going to the lowest impedance point of the circuit.

Using this method, the least amount of noise will be heard from the Signal Tracer when the negative lead is attached to the outer foil and just the opposite if the leads are reversed. I found as the capacitance values increase, using a 600 to 1000 Hz signal seemed to improve the accuracy of the testing.

Signal Tracer Circuits:

RestoreOldRadios (Don):



Bob's (Robert Gibbons) Channel:

Doug's Channel:


Crosley Radio, Model 718-B; Cabinet 8H from 1938.

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The playlist for the series:

Capacitor Outside Foil,Capacitor Polarity,RestoreOldRadios,Vintage Radio Repair,Radio Repair,Antique Radio Repair,Capacitor Testing,How to Identify the Outside Foil of a Capacitor,Crosley 718,Crosley 718B,Where to Connect the Outside Foil on Capacitors,Determing Capacitor Outside Foil,Capacitor Outer Foil Test,Are Your Capacitors Installed Backwards,Capacitor Shield Finder,Capacitor Polarity Test,Outer Foil of a non-polarized capacitor,