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? https://farm5.staticflickr.com/4757/...96ec4d5b_z.jpg Now that it's a Zombie Tube, how do I keep my other tubes safe? |
A tube with low emission coming back to life after being heated for a while is quite common. It does seem to be some kind of contamination being cleaned off a long-dormant cathode coating. This is especially common with CRTs.
The H-K short going away is more unusual, and I would be worried about it coming back. Try banging the tube around a bit while testing to see if you have an intermittent. |
I do rattle tubes when testing them. These two seemed OK, but I put them away with a note about their history.
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Just keep it away from any fresh brains, you should be fine.
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Good old days of the Friday evening horror movies on TV. :scratch2: |
It was Dracula that wouldn't have a reflection from a mirror. Also Dracula hissed and howled when a crucifix was shown in his face lol.
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