EL-84 blue glow???

rudedogg

AK Member
25657CA2-C3AC-424B-8D1C-0B538AAA0DBE.jpeg here is something I never saw before. These Sovtek EL84m have a bright blue glow that emanates from the little holes in the plates. I know this is common in KT88s and other larger bottle tubes, but this is the first I have seen it in 6bq5 type tubes. All four tubes in my EA-2s do this
 
I'm not sure what causes this, but I know this typically indicates a happy tube! The EL84m is a bit more rugged then the typical El84. Enjoy!
 
yeah all of my Russian tubes do that. As long as you're not seeing bright spots on the screen grid its fine.
 
View attachment 1308818 here is something I never saw before. These Sovtek EL84m have a bright blue glow that emanates from the little holes in the plates. I know this is common in KT88s and other larger bottle tubes, but this is the first I have seen it in 6bq5 type tubes. All four tubes in my EA-2s do this
Some tubes do this and it does not indicate any problems. Here is a pair of Bendix 5992 showing the eerily ghoulish glow......Happy Halloween!DSC05665.JPG
 
The blue color indicates collisions between high-energy electrons and various elements, including metals, residual gas, and even the glass itself. Remember, not every electron contacts the plate and politely exits the tube; some go astray on the long journey to the plate, hanging out with a bad crowd, hitting the tube structures, while others bounce off the plate and ricochet around, eventually escaping and contacting the glass which is stimulated to glow. So the blue glow can arise in a number of ways.

Given how common the blue glow is, and the fact that the tubes test good, it is unlikely to be residual gas. Since the glow is in a particular spot related to the plate, that indicates a consistent path for photons emitted by the plate, but also electrons bouncing off the plate and hitting a structure or the glass stimulating emission. (The richochet phenomenon is why tetrode kink arises, and why the suppressor was created.) The blue color suggests possible emission from a structure made from fernico (tradename Kovar), an alloy primarily of iron (Fer from ferrous), nickel (Ni), and cobalt (Co) (hence the name), which possesses a low thermal coefficient of expansion. The trace cobalt will glow blue when stimulated. It might also be the glass.

In mercury rectifiers the gaseous mercury emits in the ultraviolet, so the low end of the spectrum glows a beautiful violet-blue color. But that is a totally different phenonenon.
 
When I look closely at the "blue", it looks like soft clouds NOT attatched to the glass but hoovering just slightly away from the glass in a sort of layer.
I've tested them for any gas on more than one tester and found zero gas.
Most of the "blue" tubes I've seen are Russian. And always power output tubes.
 
On the el84 and upon closer inspection of an el34 amp I have, this is a lighter blue glow emanating from the small square openings in the plates. Not the deep blue I see in my kt88 and 7408 amps... I suppose it’s normal?
 
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