Not sure if this is a problem

[peaves_01]

I've had my crack up and running for a few weeks now, sounds awesome and everything is good regarding resistance/voltage checks.

I recently got a batch of mixed used tubes (mostly 6080s, but a few 6as7g as well) and since I've been messing around rolling them all I noticed that when the amp is turned on there is a bluish glow that seems to come from in the middle of the plates somewhere and is visible in patches on the glass. This only lasts for 2-4 seconds and then the patches shrink and disappear just before the main large filaments (heaters?) begin to glow. It's most visible when done in a dark room, possibly why I didn't notice it early on.

It has happened with all the tubes including the one supplied with the crack, so I am not too worried, but I just wanted to check if this was indeed normal for these tubes to do as I have no previous experience with tubes.

Cheers

[Maxhawk]

http://www.jacmusic.com/techcorner/ARTICLES/English-neu/blueglow/blueglow.htm

[peaves_01]

Thanks I had a look through that. What's happening with mine seems to most closely fit "type 2" fluorecence, except for the fact that it dissipates much faster. Apart from this the tubes appear to work fine, so hopefully this is the case and there is nothing actually wrong with them.

[pduk]

Mine does exactly the same thing with some (not all) 6080s. I actually rather like the effect! It's been running like this for many months, so I wouldn't worry about it 

[Grainger49]

I did a quick search for "Tube Blue" and got 5 pages of results.  It is established that this happens and has no effect on the sound.