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Swapping is the best if you have the spare tubes. Recently, I was working on a couple AA5 radios from the 1940s. Once I powered them up, they both had horrible hum even though I had changed the filters. I had checked the 50L6 output tubes on a late 1940s Hickock GM tester that uses a neon light for shorts test. They both looked ok. However, if I used a different 50L6, the hum went away. I then tested the humming 50L6s on my more modern Eico tester that applies 70 volts between the heater and cathode. They humming 50L6s leaked horribly. Goes to show that the old Hickock is not the best in at testing all possible issues.
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05-05-2010, 09:29 PM
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