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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.

These are:

  • 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):

enter image description here

And here are the old ones:

enter image description here

And here are where 11/12 and 331/332 are on the schematic for the unit:

enter image description here

enter image description here

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)?

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  • \$\begingroup\$ Keep in mind that your capacitors are more or less intact, so you can research the actual marking on the capacitors. This way, you can get the datasheet and confirm any suspicions you might have. \$\endgroup\$ – AndrejaKo Mar 15 '15 at 23:54
  • \$\begingroup\$ They are non-polar (NP) capacitors, commonly used for audio coupling, as the 3u3F value suggests. Replace with same. \$\endgroup\$ – user207421 Mar 16 '15 at 0:59
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I would say that these are indeed non-polarized caps. You would want to replace them with similar capacitors. Do NOT replace them with ceramic caps.

Ceramic caps are great for many purposes but not in the audio path. Among other problems, they suffer from piezo electric sensitivity and their value can vary greatly depending on the magnitude of the DC voltage across them.

Digikey and Mouser have suitable replacements available.

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The slashed capacitor symbol with a + is apparently a Japanese variant symbol for an electrolytic; you can see it on the schematic for C1 and C13. It definitely seems reasonable to think that without the + it signifies a non-polar electrolytic.

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I see a small plus sign (+) on one of the caps in the second photo. That's your polarity indicator. The others may have the same thing but hidden from view. And yes, replace with the same thing, not ceramics or tantalums.

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    \$\begingroup\$ Negative. That's a temperature rating. I thought the same thing. \$\endgroup\$ – BB ON Mar 16 '15 at 0:01

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