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
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