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 71a, grid to plate shorts common ?

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Posts : 10
Join date : 2010-10-13

71a, grid to plate shorts common ?  Empty
PostSubject: 71a, grid to plate shorts common ?    71a, grid to plate shorts common ?  EmptyFri Oct 22, 2010 3:31 pm

I have a Fada 20 that has had some work done previously. The original phase splitting interstage transformer has half an open secondary. At some point, a small Stancor transformer was installed to replace the defunt original, and it too has half of the secondary open. The half that is burned out on each goes to the same 71a tube socket. That particular socket is the only one that was missing a tube when I got the set. I'm thinking someone realized the tube was a dud after replacing the transformer.

The odd part about this is that the output stage works normally with a pair of good 71a tubes installed. I get infinte resistance from grid to ground on the one tube, but the scope shows signal levels comparable to the other side that reads normally. It definitely amplifies on both tubes too because I have sound running either tube individually. Am I OK running it like this, or am I just asking for problems ?
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