[R-390] Tubes glow blue

[Scott Bauer]

OK, I noticed something interesting. I am sure most of you
already know this. If a tube is glowing blue ( besides OA2)
it should be replaced. Well, I had 2 6AK6's glowing blue. 1
was V504 and the other V603. No problem, I have a couple 
hundred of them. I install 2 new ones and they are glowing blue.
I try 2 more of another brand and they are doing the same. Crap!
I tried 4 or 5 different brands and got the same result. They 
would also glow blue when pushing the test button on my TV7.

 Something must be wrong here. These are all NOS, NIB shiny
new tubes.

 I decided to install 2 in a junker and just watch for a while. Well,
I came back in an hour and they were no longer glowing blue.

 So, for the new tubes is this gas burning off? A burn in? I have only
noticed this with 6AK6's. No others.

 Sorry if this seems off topic or an ignorant question. Maybe the tube
Guru on the list can fill me in.

 Scott