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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
viggen
838 posts
 
I've asked the same question on audiogon before. The gas that glows when "excited" is inert. You can say, if there is any trace of impurity inside the tube, then the inert gas would not glow. So, the blue is actually a desireable thing.

For more 411, do a search on audiogon and on tube faqs on audioasylum.
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.......
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