Quote:
Originally Posted by benman94
Just out of curiosity, what exactly would cause a tube to "wake up" like that? What physical change would take place to make a tube work after just heating?
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I suspect that the major effect is to evaporate contamination that has built up on the surface of the cathode after sitting cold in a not perfect vacuum.
Some other possibilities:
Bring fresh emission sites to the surface of the barium carbonate cathode coating.
Release "co-activators" from the nickel cathode sleeve into the barium carbonate cathode coating.
See "Process for Activation of Cathodes" in this link near the bottom of the page:
http://www.transene.com/cathode.html
Step 1 & 2 occur during initial processing of the CRT, on the vacuum pumping station, I believe that step 3 & 4 are repeated during the 8 Volt "hot shot" and subsequent operation of the cathode at normal (or slightly elevated) temperatures.
Try it, it usually works for me, and if the "tube is dead" you don't have much to loose.
jr