To: <amps@contesting.com>
>> Date: Sat, 16 May 1998 22:33:12 +0100
>> From: "Roger D. Johnson" <n1rj@ime.net>
>> Subject: Re: [AMPS] Gassy Tubes and Gas Arcs
>> To: Jon Ogden <jono@webspun.com>
>> Cc: amps@contesting.com
>
>> Are you sure it's gas, Jon? I seem to remember that some tubes produce a
blue
>> flouresence on the inside of the envelope when bombarded by wayward ions.
>> Many mistakenly assume the tube is gassy when this occurs. A gassy tube will
>> have the glow between the elements.
>
>Not only that, a gassy tube can also have no observable glow
>between the elements and still arc!
And somehow leave no arc-craters in the metal?
>
>Outgassing from elements is common (especially with graphite
>anode tubes),
true , however, graphite anodes also scavange gas
>seal leakage is another problem.
... an oft' a fatal one.
>
>When testing tubes, it's best to high pot them cold. Then apply power
>and get them up to operating temperature while high potting or RF
>testing them with higher than expected peak voltages.
If one is high-pot. testing a tube cold (which is the method I use), why
is the high-pot. tester connected when the tube is "up to operating
temperature"?
>
>Gassy tubes can getter themselves either through an arc or other
>gettering processes. It is common to observe a tube arc and have the
>tube test good and perform normally after the fault (sometimes those
>faults are conductive "whiskers", at other times gas).
>
>Glow tells you almost nothing, except when between the
>elements. In that case it means the tube is hopelessly gassy.
A blue glow in the space where there is supposed to be a vacuum tells me
that there is gas present.
>
>73, Tom W8JI
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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