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  • #8525
    Profile photo of Les Dickson
    Les Dickson
    CVRS Member

    Is it OK to replace a 0.002 UF 1200 Volt wax paper cap with a ceramic with the same values?

    #9212
    Profile photo of Gerry O'Hara
    Gerry O’Hara
    Keymaster

    Hi Les,

    The short answer is ‘probably'(!) – as it depends a bit on the application. The most usual places for such a higher (than usual) voltage cap in a vintage radio, ie. significantly higher than the maximum plate voltage, are across the line as a suppressor, where the additional voltage rating adds a factor of safety for it being AC with line transients superimposed, and across the primary of the output transformer, where audio transients and/or back-EMF from the transformer winding are superimposed on the plate voltage. Ceramic caps of the same voltage rating as the paper cap being replaced would be ok for either application, however, I would recommend use of an appropriately rated ‘safety cap’ type for the former. Ceramic caps, especially disc types, generally have lower reactance than paper caps of the same capacity for a given frequency and therefore can make good RF bypass caps, however, caution should be exercised if using in tuned RF applications as they have a range of different temperature coefficients and can cause frequency drift if the incorrect type is used. Indeed, a specific temperature coefficient ceramic capacitor type can be used to correct for frequency drift with temperature in a tuned circuit. Avoid the use of ceramic caps as part of the signal path in high-quality audio applications, as the capacity can actually change with applied voltage, thus introducing an element of phase distortion.

    Hope this helps.

    Gerry

    #9213
    Profile photo of Les Dickson
    Les Dickson
    CVRS Member

    Thanks so much, Gerry, for taking the time to give such a detailed answer. Much appreciated.

    #9390
    Profile photo of Don Henschel
    Don Henschel
    CVRS Member

    Years ago I threw a few of these disk ceramics in due to not finding a tubular of the correct voltage or size and they seem to work but perhaps the location I installed them in ended up just being lucky. I’m going to order in a set of the recommended polystyrene or polypropylene and replace them all in my Marconi C0M 188305 that lives in my 1950 Mercury Sport Sedan. The rest of the capacitors especially in the receiver front end in the RF, IF, Converter stages are good old reliable Mica capacitors and I have no intentions of replacing them.

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