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-   -   Zombie Tube Saga (http://www.videokarma.org/showthread.php?t=270042)

Winky Dink 01-24-2018 10:16 AM

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?

N2IXK 01-24-2018 12:01 PM

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.

Winky Dink 01-24-2018 12:15 PM

I do rattle tubes when testing them. These two seemed OK, but I put them away with a note about their history.

MadMan 01-24-2018 09:12 PM

Just keep it away from any fresh brains, you should be fine.

dieseljeep 01-24-2018 09:41 PM

Quote:

Originally Posted by MadMan (Post 3195344)
Just keep it away from any fresh brains, you should be fine.

I'm trying to remember, if Zombies are the ones that don't have a reflection.
Good old days of the Friday evening horror movies on TV. :scratch2:

Popester 01-24-2018 10:03 PM

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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