Restoration Commences on 1947 RCA Victor 721TCS

[Penthode]

Originally Posted by DavGoodlin

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Among my 21" sets, whatever Zenith used in '66 and 67' had reformed well.
BUT the two CTC-11's, 12's, 16x and 20c ALL needed the electrolytics replaced just to get rid of all the lingering issues caused.

I suspect the common ground fails and other things happen to these cans, creating high impedance connections internally due to corrosion from humidity, freezing and other factors.

Interesting as I have found similar. Mt RCA CTC-11 all of the original electrolytics were bad and had to be replaced. I replaced all apart from one supplying the B+ to the Vertical output and after a month it failed. The failure mode was opening up rather than shorting.

I have besides the 721TCS, an 8T243, 8TC271 and 9TC275. Each of the chassis mount capacitors reformed okay except for the 9TC275 under chassis mount capacitor. And my CTC5 had one electrolytic fail at turn on. But is was on the 25Hz subchassis added by RCA Montreal. The Camden mounted capacitors were excellent. (I suspected the Canadian electrolytics would fail as the leakage approached 1mA after reforming at full rated voltage whereas the Camden capacitors were at or under 100uA.

I think the takeaway here is after reforming, testing at full rated voltage or 10 % above, leaving it connected for aat least 30 minutes at this state (to check for thermal runaway) and ensuring the leakage remains no higher than 200uA. And of course after this it retains it's specified capacitance. If it can survive this punishment, then it will be okay in service.