> Per the 4-400 gassy tube post, if the heater is
>operated at normal voltage for some time, wouldn't a "burn off" of any
>oxygen or gas occur? Although the vacuum might be "softer", would some
>"getter" action happen from the high temp of the filaments?
Depends on how much gas. Things like 826's can be very spectacular -
they leak like sieves - and you can literally get a cloud of smoke as
soon as you power up the filament as it burns away. Some manufacturers
recommend running the tube with filament only for about 10 minutes when
first bringing it into service, or when it's been out of service for a
while.
Some of the 'conventional' structures with pinches seem better than the
'flat bottom' seals in 4-250's, but as the tubes are less efficient, (eg
860) you don't win. The 832/829/826 form of construction seems very
prone to leakage, although probably most of those tubes are now 50+
years old. Still, my 6L6G's are over 60 years old, and they're still OK
on emission and gas.
73
Peter G3RZP
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