thanks, Gerry. Some helpful hints here.
Gerry OHara wrote:
It is of course possibe to guesstimate the value of many capacitors in a radio and thus get it working (albeit without necessarily retaining authenticity) – depending on its position in the circuit, eg. 0.01uF to 0.05uF for RF screen, cathode decouplers and plate supply decouplers, 0.05uF to 0.1uF for IF screen and cathode decouplers, 8uF for power supply filter capacitors in 1930’s models (16uF to 50uF for 1940’s and later models), 0.01uF to 0.05uF for audio stage coupling capacitors etc. The only capacitors that may be a problem to determine are those in the tuned stages (local oscillator, RF stage), but these are usually silver mica and rarely cause problems. Even in these cases the value can be estimated with some study of the circuit or even by experimentation using a variable capacitor (eg. trimmer) and once the value is found, replacment of the trimmer with a fixed value capacitor of the correct value (you will need a capacitance meter to check the value of the trimmer). Care should be taken to ensure that the replacment capcitor(s) is of the correct working voltage (to be on the safe side, use 630v plastic film types and 450v electrolytics (except for audio stage cathode bypass applications where 50v will often suffice).