Pat Barthelow wrote:
Is the location of the glow important? I used to see Blue glow on the
inside glass of 4-400A amps, and was once told that this is normal, and
not indicative of Gas in the tubes. It was some kind of interaction of
high velocity electrons with the glass. (kind of like Cherenkov
Radiation?) Gas glows have to occur in between the cathode and the
plate.....Is that correct?
Yes. The blue glow on the inside of the glass is due to stray electrons
hitting the glass, and you see something similar through the ceramic of
some tubes.
A gas discharge occurs in what should be empty space *between* the
electrodes.
From: "Ian White, G3SEK" <G3SEK@ifwtech.co.uk>
Reply-To: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
To: amps@contesting.com
Subject: Re: [Amps] a BANG in the AMP ?
Date: Mon, 20 Oct 2003 09:14:30 +0100
Bill Turner wrote:
Blowing the fuse, which IIRC is what happened to the original poster.
I had that happen once in my SB-1000 that had sat for about four
years. As soon as I turned it on there was a bright flash, a loud pop
and the AC fuse blew. I used a variac to bring up the AC slowly and
it was apparent the tube had become gassy. Very pretty purple glow
Purple is due to nitrogen - a pretty reliable indication of an air
leak. Oxygen is there too, of course, but the bluish colour tends to
be masked by the purple.
Outgassing of the tube's structural materials can also involve
nitrogen, but it wouldn't normally be so predominant, so you'd tend to
see more of the blue.
(BTW, these observations come from some years of leak-tracing in glass
and metal vacuum systems, using a hand-held Tesla coil to strike a
discharge inside the glass parts. The color and intensity of the
discharge can tell you a lot.)
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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