Hi Gary,
There are varying degrees of vacuum. I don't have my Vacuum Technology
books here in the shack, so I won't go into details about where the line
is drawn between "High Vacuum" and "Super High Vacuum" and what level of
vacuum is needed in power tubes, because my memory on the details is not
that good and I'm sure I'd get it wrong. In any case I do know there is
no such thing as a perfect barrier or seal to gas molecules. Much as a
latex balloon loses it's pressure, metals and glass both allow gas to
leak through at a slow, yet measurable rate when measured over long
periods of time.
I'm sure there is someone else on this reflector who can tell you more
about getters. I do not think that getters are "spent" the first time
the tube is fired up in the factory, they continue to function
throughout the tube's life in order to counteract the slow, inevitable
leakage through the glass. I'd sure like to hear a more authoritative
account of that. Anyone know?
DE N6KB
First of all, I thought a tube was supposed to be pumped down to a very good
vacuum and then completely sealed. Thus there should not be gas leaking in.
It should not accumulate over time. If it does, its gone bad. Is this not
so ?
Secondly, I thought the getter was used once, when it was "fired" at the
factory. I did not believe that it was at all functional beyond that single
use. Is this not so ?
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