[Arran]

I think C1 is maybe 600 volts, I can't see why an 800 volt cap would be needed there at all. On occasion they will use a high voltage cap across the primary of the output transformer but I've only seen this in an AC set with much higher plate voltages then the usual 90-110 you see in an AC/DC set. I noticed they used a 700 volt job on the coupling cap for the volume control, C7, that was for leakage, the plate voltage on the 12SQ7 is maybe 60 volts tops, no where near 700 volts.
Regards
arran