WEE Technology Company Limited - WEE are Capacitors Specialist

Except for outer foil marking on the surface of the capacitors, some factories make their capacitors apparently have a shorter lead on the outer part of the foil. If I havent totally got this wrong it is suggested that the outer part of the foil should be connected to the negative side.

The outer foil end is connected to the lower impedance side, in a signal situation like inter stage/coupling this would mean the outer foil end is the input side (previous stage). In a decoupling situation the outer foil end goes to ground (lower impedance).

If you can not identify the outer foil of the capacitor by external appearance, and you also do not own an oscilloscope, we suggest you try below link and find other ways to identify film capacitors directions.

https://forum.audiogon.com/discussions/are-film-capacitors-directional

I've found it much easier to discern the orientation of the outer foil on film caps using TrueRTA spectrum analyzer software on my laptop. The most expensive version of this software (1/24 octave resolution) is only $100, lower resolution versions cost less.

I use the line in connection on the laptop with a simple cable consisting of a mini jack on one end and bare wires for signal and ground on the other, then watch the 60Hz peak on the spectrum analyzer go up or down depending on cap orientation. I also own a Tektronix 20 MHz scope and the TrueRTA method works much better for me.