My appologies Ian ,your correct . I do know a lot of amps speced the voltages to +/- 20% ,but 20% on heaters would be a little to much margin under most circumstances .I have seen a 6au6 cathode follower in a tube mic 20% under on the heaters but with low ht volts as well .
If the unit wasnt used for a long time it might be worth allowing the electrolytics reform, the usual way of doing this is to slowly raise the supply voltage through a rotary auto transformer. In any case you have them powered up now and their working ,theres a likelyhood the caps could either improve to some degree or just continue to become less and less effective ,if your heater volts seem to be slowly drifting up over time you could assume the caps are making a bit of a recovery ,if the voltage is slowly getting less and less ,Id assume the caps are finished . If the volts hold stable and everything is hunky dory your 70 year old caps might even be within their spec which could easily be +20/-50% .
If the unit wasnt used for a long time it might be worth allowing the electrolytics reform, the usual way of doing this is to slowly raise the supply voltage through a rotary auto transformer. In any case you have them powered up now and their working ,theres a likelyhood the caps could either improve to some degree or just continue to become less and less effective ,if your heater volts seem to be slowly drifting up over time you could assume the caps are making a bit of a recovery ,if the voltage is slowly getting less and less ,Id assume the caps are finished . If the volts hold stable and everything is hunky dory your 70 year old caps might even be within their spec which could easily be +20/-50% .
