I'm currently in the process of restoring a 1960's phonograph made by Zenith. My plan is to replace all the capacitors among other things. I have the original schematic, purchased from Sam's Technical Publishing, and am currently placing an order for the necessary capacitors.

The schematic lists the capacitors and their respective capacitance and voltage ratings. However, for some reason, it lists electrolytic capacitors and fixed capacitors separately. I'm under the understanding that electrolytic capacitors are fixed capacitors. Am I incorrect? To add to the confusion, the actual schematic shows many of these "Fixed Capacitors" as being polarized. Do I need to buy, for example, ceramic capacitors to replace the fixed capacitors? Here's 3 pictures of the schematics showing the capacitor listings and their counterparts on the schematic: HERE

  • \$\begingroup\$ That is probably a company practice, I see no reason to do that other then convince. \$\endgroup\$
    – Gil
    Commented Apr 11, 2023 at 2:42
  • \$\begingroup\$ Conventions in the 1960s were probably different than today. \$\endgroup\$ Commented Apr 11, 2023 at 2:49
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    \$\begingroup\$ That schematic was drawn before the Greek alphabet was invented, so "m" = micro and "mm" = pico. C7 is 30 pF and C21 is 820 pF. C1A is 150 uF. \$\endgroup\$ Commented Apr 11, 2023 at 3:12
  • \$\begingroup\$ Perhaps they classify three types of capacitors: electrolytic, variable, and fixed. I would not consider those schematic symbols (curved one side, straight on the other) to imply polarization of the cap. Note that two of the electrolytics (3 uF) are non-polarized. You can find nonpolarized 3 uF capacitors, or you can connect two 6 uF electrolytics in series, back to back, as a substitute for each. \$\endgroup\$ Commented Apr 11, 2023 at 4:04
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    \$\begingroup\$ It makes no sense to replace all caps, including the non-electrolytics. Either restore only what is broken, or make a clone with all new parts (caps, resistors, diodes, transistors, pots, and all other parts you intend to replace anyway). \$\endgroup\$
    – Justme
    Commented Apr 11, 2023 at 5:09

1 Answer 1


The fixed does not mean the opposite of variable.

There are capacitors with liquid electrolyte which is not solid or fixed, and then there are capacitors that don't have liquid electrolyte, for example plastic film or ceramic capacitors.

So in this list the fixed capacitors mean all non-elctrolytic caps. Some of them are specifically marked to be of N75 type, which is an old Class 1 ceramic not really used today. The types of the other caps are not specifically known but they might be plastic caps.

As ceramic, plastic, and other types of caps are used for their properties that make them suitable for a specific task in the circuit, don't blindly change the type of the capacitor unless you know what you are doing.

Don't e.g. change all non-electrolytic caps to ceramic or plastic.

Only a couple of the electrolytics are special non-polar type.


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