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[Amps] Ionized Gas in the Tube

Subject: [Amps] Ionized Gas in the Tube
From: "Pat Barthelow" <>
Date: Mon, 20 Oct 2003 17:55:08 -0700
List-post: <>
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?

Pat Barthelow

From: "Ian White, G3SEK" <>
Reply-To: "Ian White, G3SEK" <>
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 inside. :-)

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' _______________________________________________ Amps mailing list

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