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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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10th Dec 2013, 4:44 pm | #1 |
Heptode
Join Date: Jul 2012
Location: Derby DE1, Derbyshire, UK.
Posts: 626
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Valves with glowing envelopes
Hi all,
I dare say there are many reasons as to why a valve may emit a glow within the glass envelope, but what are the most common reasons for the occurrence of a red, blue, pink, or salmon coloured flame or fire, within the valve tube? (I don't mean when the whole of the grey column glows red hot like a bar fire) I mean when you can clearly see a pulsating flame within the valve tube. Any answers welcomed. Thanks, Paul. |
10th Dec 2013, 5:32 pm | #2 |
Dekatron
Join Date: Aug 2003
Location: near Reading (and sometimes Torquay)
Posts: 3,086
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Re: Valves with glowing envolopes
A glowing mass in the empty space inside a valve is caused by the ionisation of gas. The question is why, and it depends on the valve.
Some valves are meant to do this and glow brightly. These are mainly voltage stabilisers and are most often neon red but some glow blue. Thryratrons also glow when conducting. High power valves produce some glow due to residual gas in the vacuum, but it should not be too bright. Any valve being massively overloaded is likely to do this too. Finally, valves that have gone "soft", i.e. some air has leaked in, will glow and this is a bad sign. |
10th Dec 2013, 6:01 pm | #3 |
Hexode
Join Date: Jan 2013
Location: Ă…lesund, Norway
Posts: 361
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Re: Valves with glowing envelopes
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10th Dec 2013, 6:04 pm | #4 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
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Re: Valves with glowing envelopes
But if you genuinely have a 'valve with a glowing envelope' i.e. it's the envelope which is glowing, not the space within it, then that is fluorescence from trace elements in the glass. It tends to occur more commonly in large-ish power valves.The fluorescence is caused by stray charged particles (almost entirely electrons, I believe) hitting the glass. Blue is far and away the most common colour. It's nothing to worry about.
Cheers, GJ |
10th Dec 2013, 6:27 pm | #5 |
Heptode
Join Date: Jul 2012
Location: Derby DE1, Derbyshire, UK.
Posts: 626
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Re: Valves with glowing envelopes
Hi GJ, hi Anthony,
It was one of those small PCF802 TV valves doing it once, I noticed a salmon coloured flame inside it and then the next time it was swiched on I think the HT went down, well anyway the screen went blank. But it was a long time ago and I just wondered what the cause of the flames were. Paul. |
10th Dec 2013, 7:42 pm | #6 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
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Re: Valves with glowing envelopes
Almost certainly gas (air) inside the envelope which lead to internal arcing.
Cheers, GJ |
10th Dec 2013, 7:45 pm | #7 |
Heptode
Join Date: Nov 2004
Location: Ripon, N.Yorkshire, UK.
Posts: 782
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Re: Valves with glowing envelopes
EF91s glow prettily sometimes, especially when used as RF Oscillators.
Jim |