[Milsurplus] How Much Vacuum in "Vacuum Tubes?"

[C. Whitaker]

de WB2CPN
Back in WWII the underground forces in Europe,
mainly Eastern Europe, rebuild tubes for their
hidden radio equipment.  All that had to be
replaced was the filament and cathode.  I recall
that a critical operation was "lapping" the
base and envelope of miniature tubes so that they
would require a minimum of heat to fuse. And, in
some applications of high-power tubes the vacuum
was maintained with a pump even when the tubes
were in operation.  Trivia.    73   Clete