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Old 01-24-2018, 10:16 AM
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Winky Dink Winky Dink is offline
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Join Date: Apr 2010
Location: Meridian, Idaho.
Posts: 583
Zombie Tube Saga

In the course of my most recent project, the radio under test started sounding weird, then went silent. I found an accidental short which apparently killed my only 2A5. I tested the tube and found all to be OK except it showed zero transconductance. I rechecked the settings, retested, then tested on an emissions tester. Same result. Zero emissions. So I set it aside.

In the next few days I acquired three used 2A5's. Two tested OK, but the third showed a heater/cathode short on the transconductance tester. Retest after a five-minute warm up gave the same result on both testers. So I set it aside.

Four days, before tossing the cathode/heater short tube, I decided to check it again. I put in the tester, turned it on, and forgot about it. A hour later I looked at it, and it showed no leak, no short, and excellent transconductance. So, it was a self-healing tube. Probably got something on the cathode or heater which took a while to burn off.

Then I thought, what the heck, I'll retest the dead tube. Son of a gun, it was normal too. This was good fortune, but also eerie. How did it come back from the dead?



Now that it's a Zombie Tube, how do I keep my other tubes safe?
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