I agree completely!
The only time I've had Eimac tube gas issues, has been with WWII era
250THs and 100THs.
The ONLY reason for this to occur is because they are NOT force air
cooled! They are ONLY convection cooled.
The 3-500s, 4-400s, 3-400s, 3-1000s, and 4-1000s are all in a forced air
socket to keep that seal between glass and pins cool, and take away the
envelope heat out through a chimney. Then there is the plate cap. It
also takes the heat from the plate and removes it in the air stream.
The 813s and 572Bs aren't as well cooled, BUT - really don't need to be.
Bob - N0DGN
On 11/6/2011 1:09 AM, Fuqua, Bill L wrote:
> I have quite a collection of power tubes. Many built 50 or more years ago.
> I rarely find
> gassy tubes. I have trouble with the idea that air leaks thru the envelope of
> glass tubes.
> I suspect that if a small amount of air does get into the vacuum it is from a
> virtual leak.
> These are due to tiny gas pockets or bubbles in seals or defects in the
> internal metal parts.
> I is a common problem in research high vacuum systems. The gas does not
> come from the outside
> thru the glass but from a flaw in the glass or other material that holds a
> small amount of gas after
> the tube is pumped out.
> If a 60 or 70 yea old large power tube still has a hard vacuum I think it
> is unlikely that air is leaking thru
> the glass.
> 73
> Bill wa4lav
>
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