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!
Outgassing from elements is common (especially with graphite
anode tubes), seal leakage is another problem.
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.
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.
73, Tom W8JI
w8ji.tom@MCIONE.com
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