11-17-2016, 08:51 AM
Are you replacing the transformer with the identical type each time?
Its possible there is a manufacturing defect at the termination of the secondary winding with the lead wire. The winding is made with very fine and delicate wire and it only takes a little corrosion at the joint to have it fail. The fact that the transformer seems to fail intermittently at first seems to support this idea. If all three transformers were the same type and failed similarly, then this would be my guess.
Really, the most likely external cause that could make the secondary fail is a grid to plate short in the corresponding 71A tube. As you have already changed the output tubes, and still had failure, then it probably is something else.
I would try another interstage from a different manufacturer.
Its possible there is a manufacturing defect at the termination of the secondary winding with the lead wire. The winding is made with very fine and delicate wire and it only takes a little corrosion at the joint to have it fail. The fact that the transformer seems to fail intermittently at first seems to support this idea. If all three transformers were the same type and failed similarly, then this would be my guess.
Really, the most likely external cause that could make the secondary fail is a grid to plate short in the corresponding 71A tube. As you have already changed the output tubes, and still had failure, then it probably is something else.
I would try another interstage from a different manufacturer.
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