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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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Old 10th Dec 2013, 4:44 pm   #1
Stylo N M
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Default 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.
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Old 10th Dec 2013, 5:32 pm   #2
GMB
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Default 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.
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Old 10th Dec 2013, 6:01 pm   #3
Anthony Thomas
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Default Re: Valves with glowing envelopes

Quote:
Originally Posted by Stylo N M View Post
I mean when you can clearly see a pulsating flame within the valve tube.
Do you have a type number for the valve Paul, could it be a stabiliser tube like an "OB3" or similar?
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Old 10th Dec 2013, 6:04 pm   #4
GrimJosef
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Default 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
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Old 10th Dec 2013, 6:27 pm   #5
Stylo N M
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Default 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.
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Old 10th Dec 2013, 7:42 pm   #6
GrimJosef
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Default Re: Valves with glowing envelopes

Almost certainly gas (air) inside the envelope which lead to internal arcing.

Cheers,

GJ
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Old 10th Dec 2013, 7:45 pm   #7
jim_jobe
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Default Re: Valves with glowing envelopes

EF91s glow prettily sometimes, especially when used as RF Oscillators.
Jim
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