[Amps] Re: Ionized Gas in the Tube

[Ian White, G3SEK]

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 at ifwtech.co.uk>
>>Reply-To: "Ian White, G3SEK" <g3sek at ifwtech.co.uk>
>>To: amps at 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