Mike

These are 'varistors' or voltage dependant resistors which are used as
transient suppressors. In my 'chinese copy' of the Decca bridge PA, I
used a 200 volt, 8 Kilo-amp, 85 Joule device available from Farnell
P/No: 502-224. It is also a red disc and is about 25 mm diameter.

73, Tom G3OLB


Mike, G3XDV wrote:

A component across one of
the transistors burnt out. I have a diagram but do not recognise the symbol
(perhaps a temperature variable resistor?). It is called R31V and the symbol
looks like a preset potentiometer, but it looks just like a red disc ceramic
capacitor.