In a message dated 06-20-14, Tom Walker said to Ed Vance:   
      
   Hi Tom,   
      
   TW> Speaking of "Final" Tubes I rembember from the 50's when I was on a   
   TW> Submarine for the Radar the ET's they had a board with a spare set   
   TW> of Finals mounted with the filiments powered.   
   TW> Seems like the tubes needed a break in because of you put a cold set   
   TW> in and hit them with the high voltage B+ they would fail.   
      
   That is the way old (even unused) should be broken in irrespective if   
   directly or indirectly (cathode) heated. The reason is that the glass   
   feedthrough always allow some of the vacuum to escape with age.   
      
   When the tube is manufactured the getter is used to burn the remaining   
   air away but after that the getter is useless. That is the purpose of   
   the pre-heating of replacement tubes and it also concerns old unused   
   spare tubes.   
      
   CU AGN, Sam, OH0NC   
      
   aka Holger   
      
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