Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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RE: Idea for Prolonging Tube Life

Posted by unclestu (D) on March 19, 2012 at 15:34:44

In Reply to: Idea for Prolonging Tube Life posted by CJ Larson on November 29, 2011 at 19:58:17:

Actually a lot of the internal contamination comes from contaminated parts: glass as well as the metal work. Sulfur comes from the lubricants used for drawing wires and rods, The metal and glass itself have dissolved molecular gas imbedded in them, typically the lighter gasses.

In the old days, precision military types all went through a pure hydrogen bake out in order to reduce the oxides, in particular. The oxides and hydrogen are responsible for the cathode "poisoning". The nitrides don't help any either. The hydrogen bake(pure hydrogen at 1200 degrees) out insures that all heavier gasses are displaced by hydrogen, which is then easier to pump out.

Glass is slightly hydroscopic, and thus an acid wash helps eliminate some of that contaminated surface.

Hydrogen bake outs are rarely utilized today. The NOS types are thus much lower in vacuum after use than most modern manufacture, with a few exceptions.

Of course YMMV

Stu

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