I am restoring a stereo amplifier circa 1985 (specifically the Technics SU-Z55). Part of that is replacing the electrolytic capacitors on the mainboard due to some audio popping and general age. There are 6 capacitors on this board that are electrolytic but have no polarity strip on them or negative marking on the PCB.
- C11: 1uF/50V
- C12: 1uF/50V
- C331: 3.3uF/25V
- C332: 3.3uF/25V
- C403: 47uF/16V
- C409: 47uF/16V
On the board, they are marked with a special kind of capacitor symbol I am unfamiliar with (caps removed):
And here are the old ones:
And here are where 11/12 and 331/332 are on the schematic for the unit:
If I had to guess, I would say these are some kind of non-polarized electrolytics, but I've never heard of such a thing and don't want to bet my amplifier on a hunch. What are these capacitors, and is it okay to replace them with a non-polarized cap of the same value (like a ceramic)?