New WE 300b's blue glow

[TubeHound]

Hi,

I just bought a couple of WE 300b's for my monoblocks. I urgently opened the nice blue boxes and installed them in my amps, replacing a pair of Svetlana 300b's.

I turned the power on and both tubes have the blue corona at the top of the glass.

I did a search here and found out, ( I hope), that this is normal for new tubes and will/should lessen as the getters do thier job and eliminate most of the gas molocules left from the construction process.

I quess I just want to be reasured that I not damaging the most expensive tubes I have ever payed my hard earned cash for.

There is no blue glow inside the filament area, just at the tops and it does look cool.

[Colt45]

Is it actually *on* the glass?

Some glass glows (usually bluish-purplish.. ive heard of green though) when its struck by stray electrons. This is not a problem, and neat looking too!

[fdegrove]

Hi,

I quess I just want to be reasured that I not damaging the most expensive tubes I have ever payed my hard earned cash for.

While I don't find this "normal" it shouldn't be problematic in the long run.

The getters will burn this remaining gas off within a month or so.

Cheers,

[valveluver]

The tubes are gassy. They have probably lost vacuum. I would just burn the filaments, at about 70 percent voltage and it MAY fix the problem. The tube will not meet specification with gas.

[Gabevee]

IF it is gas. I have tubes that are quite broken in and still glow blue.

Gabe

[Morse]

Hi maybeim;

I agree with GabeV FWIW. Your description is consistent with excitation of phosphorescent materials in or on the glass envelope rather than excitation of stray gas molecules. If it is a gassey valve, you will see a diffuse blue glow with no sharply defined borders that is in the space INSIDE the glass envelope. If it is just electron excitation of phosphors on the glass, the blue glow will ONLY appear on the inside surface of the glass (and also possibly on the inside surface of the plate structure for the same reason).

Good luck and all the best,
Morse

[The-Planet]

The blue fluorescence at the inside surface of the glass bulb is typically seen with a very good vacuum. A gassy tube will have a blue glow around the filament/grid structure and will draw excessive grid current.

Enjoy the light show, not a problem at all.

[dhaen]

Hi The Planet,

Originally posted by The-Planet
The blue fluorescence at the inside surface of the glass bulb is typically seen with a very good vacuum. A gassy tube will have a blue glow around the filament/grid structure and will draw excessive grid current.

Enjoy the light show, not a problem at all.

I'm sure you're right.
BTW I notice that was your first post. Welcome to the Forum
Why not tell us something about your interests either here or in the Introductions section?

Cheers,

[SHiFTY]

I have some 6V6EH that have been used for a year or so, and have a blue glow, it is entirely normal. They have not changed much since they were new. If you look closely, it is definitely the glass that is fluorescing. (I guess due to secondary electron emission? Bonus question for the physicists! ) The central plate/grid/cathode structure has no glow around it.

I think part of the reason that old tubes are so often coated with grey or black paint inside is to remove this glow, so people wouldn't think the tubes were gassy...

As an aside, I found a tube the other day with a bubble in the glass! Is this likely to fail? I already broke the "outside" of the bubble, guess I should be more careful...

[fdegrove]

Hi,

I think part of the reason that old tubes are so often coated with grey or black paint inside is to remove this glow, so people wouldn't think the tubes were gassy...

No, that was not the reason.
From memory, I think this had to do with a sensitivity to UV light.

As an aside, I found a tube the other day with a bubble in the glass! Is this likely to fail? I already broke the "outside" of the bubble, guess I should be more careful...

It's a weak spot alright, you'll know when it start to leak.


Cheers,