Restoring a RCA 21CT55

[etype2]

Originally Posted by benman94

Keep digging. A 21-CT-55 flyback can kick out 30+ kV unregulated. Is your fly damaged?

If it is, I'm going to suggest something that is anathema to most around here: use a solid state HV supply. The set is not working correctly in the first place, so originality doesn't count for jack at the moment.

A solid state HV supply would get the set performing closer to how it was designed.

Best of luck in either case.

We thought the fly was toast initially when the failure happened. We measured only 10KV. The thought was the fly was still good otherwise it would measure zero. It turned out to be an open resistor. I’d just like to have a good spare. Best chance for that is finding another 21CT55.

[benman94]

Originally Posted by etype2

We thought the fly was toast initially when the failure happened. We measured only 10KV. The thought was the fly was still good otherwise it would measure zero. It turned out to be an open resistor. I’d just like to have a good spare. Best chance for that is finding another 21CT55.

What I'm driving at here is that 21 kV is not at all normal for a 21-CT-55, and is not good enough. The Hoffman I sold to Nick would uses the same exact HV section and would crank out 30 kV or more with the shunt pulled. Something has to be loading down the HV, my guess is that there's still some issue with the 6BD4A or the associated circuitry. Don't throw in the towel on the HV issue, and DO NOT run the set until it is properly fixed. Droopy HV could also be failing HV caps which WILL take out your flyback.