[R-390] Gettering old tubes

2002tii bmw2002tii at nerdshack.com
Wed Mar 2 15:01:47 EST 2011


Ben wrote:

>maybe put together a chassis with multiple sockets and a filament 
>supply to keep your tubes warm

Filaments alone won't even get the envelope to full operating 
temperature, so this would only be better than storing them at room 
temperature if you did it constantly for all of your spare 
tubes.  And then, you'd have to worry about (i) the decreased 
in-service heater life due to the "storage" operation of the heaters, 
(ii) "cathode interface," and (iii) the deposits of cathode oxides 
boiled off and deposited on the grid.  When the tube is operating 
(drawing plate current), most of these boiled-off cathode oxide 
molecules are moving too fast to deposit on the grid.  When the tube 
is cut off, they are drifting slowly and tend to deposit on the 
grid.  Cathode oxides on the grid lead to grid emission and thermal 
runaway when the tube is operated.

Best regards,

Don



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