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Blue Glow in Vacuum Tubes

PostPosted: Wed Jul 21, 2004 7:43 am
by arnoldc
There are a few types of blue glow in Vacuum Tubes.

1) FLUORESCENCE. This type of glow is normally dark blue. It can appear outside the anode, on the glass surface inside the bulb, and as spots on other parts inside the tube. The spots may have the appearance of stains. With very used tubes, you can sometimes see a faint stain on the glas, at the position where the fluorescence appears. In most cases, you will find it with power tubes. It results from electron bombardment on glass taking place within the tube. It generally has no negative effect upon the performance, and in fact, tubes displaying this phenomenon are particularily good with respect to having a high vacuum. Mesh plate tubes will display this blue glow under high Anode current, since these have holes in the Anode, letting electrons pass. You may also see it in tubes like EL34, or 6550, which have holes in the anode. These holes are for adjusting the grids during production. Typical for this kind of glow is, that if you hold a conductive surface against the fluorescent spots, (if on the glass) the spot will change it's shape. (The electrons take a differnent path)

2) GASSY AMPLIFIER TUBES. These produces a white-blue haze, of low brightness, inside the Anode. (The color is like this: ====== ) You can best see it, when looking from the top, inside the tube. The brightness is much less than the filament lighthing. You can only see it in a dark room, and it appears as a uniform cloud, no spot building. It is this kind of blue glow that indicate the vacuum is not as good as can be. The electrons on their way from the Cathode to Anode hit gas molecules, that get ionesed from the incidents. The recombination of Ions and Electrons produce the light effects. The Gas iones are much heavier than electrons, and hit the Cathode with a considerable amout of energy. This causes early wear-out of the cathode, and grid current if it gets worce. The tube will self destroy eventually.

3) REGULATOR AND THYRATRON TUBES. These tubes are high vacuum , but there is a residue of gas added to the tube, on purpose. They light up pink, violet, or orange, depending on the used gas, like Crypton, Neon, etc.

4) MERCURY RECTIFIERS. These light white-violet, and have a mercury gas residue. The glow indicates proper operation. Used tubes may look worn out and extreme dirty, but can be 100% ok still.

Taken from JacMusic website. Original page is Here

PostPosted: Wed Jul 21, 2004 10:13 am
by KD
I have seen the blue glow in Sovtek 2A3 (inside the glass in the neck part) and the 300B-98C which came with the Tono amp (on the mica spacers).

Which tubes have you used that have this glow?

PostPosted: Wed Jul 21, 2004 10:29 am
by arnoldc
My Sovtek 2A3 does too, pero isa lang :? Also my RCA 5U4-G

I will see about the RCA 2A3 tonight :D

PostPosted: Wed Jul 21, 2004 10:59 am
by rsm2a3
My RCA 2A3 (JAN) with blue glow, and i remember my philips 6L6 (JAN) for my MC240.

PostPosted: Wed Jul 21, 2004 6:23 pm
by jadis
It's the Telefunken ECC82 in my Jadis JPL line stage that has the bluish glow. But
one smooth plate Tele82 does not have it. In right, it's a bit bright orangy. Different
construction, it seems.

PostPosted: Thu Jul 22, 2004 4:52 pm
by John Martin
My Svetlana and Sovteks EL34 emit this blue color also. Cool!!!!!!!!!!!1

PostPosted: Thu Jul 22, 2004 5:15 pm
by jadis
rsm2a3,arnoldc,John Martin,

glad to know that we are all in the 'blue club'. actually my bluish <>82 has been
that way for the last 7 years.

PostPosted: Sat Jul 24, 2004 8:39 pm
by jadis
I just remembered, in the mid 80s, the GE 6550s of my ARC-D115
amp had blue gas that actually danced around when transients occur...
such an amusing sight. But I have not seen that occurence ever again
in any other gear or tubes.

PostPosted: Sun Jul 25, 2004 1:43 pm
by arnoldc
you guys want real blue glow? try mercury vapor :twisted:

PostPosted: Tue Jul 27, 2004 6:56 pm
by Jon Agner
My electro Harmonix 2a3 and 7591s have 'em

PostPosted: Thu Jul 29, 2004 8:33 pm
by KD
What if the blue glow flickers in sync with the music (the bass lines)? Is this normal?

PostPosted: Thu Jul 29, 2004 8:48 pm
by jadis

I think so, the 6550s in my ARC D115 amp did that, when it was brand new. No
problem with that amp.

PostPosted: Thu Jul 29, 2004 8:53 pm
by KD
Cool. Dancing lights. Parang Radiowealth! :lol:

PostPosted: Thu Aug 26, 2004 10:30 am
by arnoldc
My RCA 807 :D


PostPosted: Thu Aug 26, 2004 10:54 am
by jadis

cool pic! maybe blue is a healthy color for tubes. :)

PostPosted: Thu Aug 26, 2004 11:07 am
by s2kov
The blue glow of EL34 tubes on my ST70....


PostPosted: Thu Aug 26, 2004 11:24 am
by arnoldc
is the EL34 or 6CA7? mataba ah.

PostPosted: Thu Aug 26, 2004 11:30 am
by s2kov
Fat bottle 6CA7

arnoldc wrote:is the EL34 or 6CA7? mataba ah.

PostPosted: Thu Aug 26, 2004 12:41 pm
by jadis

those are nice blue glows even on bright daylight. cool.

PostPosted: Thu Aug 26, 2004 1:18 pm
by s2kov
:) :) :)

jadis wrote:s2kov,

those are nice blue glows even on bright daylight. cool.