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floobydust wrote:

Okay, I think I understand.... and thanks for the link on the YO-186... if I can ever locate some of these I'll be sure to grab some (hmmm, a trip to Russia perhaps). As tubes get very hot internally, there were some procedures for trying to eliminate the possibility of "out gasing" from the tube elements, if they were exposed to internal heat levels beyond their ratings. Transmitting tubes were a good example as many of these had cherry red to orange anodes for CCS operation. Even the high powered VR pass tubes (6336 and 6528) had anode materials and processes to ensure "out gasing" would not be a problem when deployed in high-current applications. It's not very clear how much of this exists today with some of the new manufactured tubes.

This is one of many subjects that so much attracted by in YO186. It reported that tungsten cathodes have no such a problem (or less) but the oxide cathodes with their higher efficiency have a tendency to gas the tube. When the electrons are boiling on the cathodes it reportedly some kind of gas get created that in a long run screw the tube and the can’t be properly be absorbed by other gas-handling methods. To minimize this effect the pre-fabricated cathodes before they placed into the tubes exposed to overburning. The over burning  reportedly is some kind of sophisticated  ceremony where cathode is heated to very high temperature, much-much higher then it even will see in regular life and then submerges in some kind of cold chemical broth.  It is reportedly a sophisticated and expensive ceremony that was done in past and allegedly discarded by today makers of the tubes. So, according to my Russian sources the YO-186 was exposed for overburning three times (!!!) before the cathode was accepted for this tube. I do not want to create a myth about it but if it was true them it very much goes along with the vision that in past people did not try to save on the things that that are important.  I do not know if all of it true but allegedly the YO186 was one of the very few tubes that was exposed to triple overburning.  Perhaps the facts like this explains why some of the older tubes run for 50 years and still “measured as new” (even I personally do not support this notion)

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