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Blue Gas in Tubes - Why? Is it Bad?

My friend's Svetlana KT88s glow with blue gas. He says that it doesn't mean anything, but I'm not so sure. He claims that he has seen this in Svet KT88s from different sources, including Upscale Audio.

I have heard that companies like Audio Research screen out tubes for "gas". Is this the same thing?

Does this affect the life or the performance of the tube?
saxo
gs5556
1,234 posts
 
It's not a problem. The blue glow is caused by trace cobalt within the tube. Cobalt is a byproduct of the tooling process of sealing the glass.
saxo OP
98 posts
 
I found the following on Audioasylum.

http://users.erols.com/bluestat/FAQ/blue_glow.html

This indicates that the blue glow is normal and, as Viggen said, actually indicates a tube which is desirable.

Unless others disagree.......
elevick
2,636 posts
 
Well, since tubes are supposed to be a vacuum, why should you want any extra gas? If it were desireable, everyone would do it, not just a few rare cases.
glide3
402 posts
 
If you go to the KR Enterprise site they will tell you this is bad and will give you the reasons (I don't recall). This is the only source where I have ever heard that this is negative but as they make tubes perhaps they have a point????
dweller's avatar
dweller
3,781 posts
 
I use an ARC VT-100 with an LS-9 (ss) preamp. My tubes glow orange. I tried a Morrison ELAD (ss) preamp which made the tubes glow bright blue -I disconnedted it immediately.
I don't know if my tubes "had gas" but I wasn't taking any chances...
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