Mesa Mark IV 6l6 tube glowing neon blue?

[Josh_P]

So I fired up the Mark IV and noticed the 6l6 on the outside (far right side if looking straight on from the back) is glowing neon blue while the others have a smooth subtle orange glow about them. Does this mean I need to replace the tube or is this normal for only 1 to be doing this? (running in class A config if that matters)

many thanks,

~J

[YaYoGakk]

It's normal.
Here's a picture I took a while back.

[sleepyone]

I've read or heard somewhere that the blue glow is actually a good sign...

[kotornut]

normal in my experience.

[Josh_P]

Thanks guys!!!!

[Vim Fuego]

I don't like to disagree, but, usually a blue glow means the tube has gone "soft" this means there's now some gas in the class envelope (instead of a vacuum) and the gas is being ionized. Check http://en.wikipedia.org/wiki/Vacuum_tube the section Vacuum
The gas/air can come from many sources, minute cracks around the pins, glass being semi-permeable, poor manufacture...
Best to replace I feel.
Jim

[sleepyone]

uh.....cr@p.....I got a few here with that stupid neon glow....

[Vim Fuego]

^
I didn't mean to scare you! I suspect you can go quite some time with a dim blue glow before there are real problems, but it is certainly an early indicator, I replace if I see it.
Keep an eye on the tubes and if the plate (anode) glows orange then switch off (and replace) immediately.
Cheers,
Jim

[sleepyone]

Thx for the advice man! I'll keep an eye on those tubes hehehe