blue glow on one channel

[wicked1]

Hi,
One of the tubes in my amp has always had a blue glow. Today I finally decided to do some testing, and swapped tubes, and still, the right channel was the one glowing.
I even used a different type of tube, and same thing.

I checked the current and voltage on both channels, and they are exactly the same.

this is a 300b se amp.

What else could cause this if the voltage and current are the same?

thanks!

 

[SY]

http://www.jacmusic.com/html/articles/blueglow/blueglow.htm

 

[wicked1]

Well I know it's not gassy, and it's nothing to worry about, but I haven't found anything that says why one channel does it. It's not dependent on the tube, but on the channel.


Thanks for the link. I hadn't seen that particular site. Lots of great glowing tube pictures!

 

[m6tt]

Have you tried replacing the coupling cap? It's a long shot, but I've seen weirder.

 

[vax9000]

Would a high frequency oscillation cause the problem?

 

[m6tt]

I've seen weird loading cause blue glows otherwise unexplainable as well. Maybe back emf from a transformer?

 

[Jeb-D.]

It's normal for some tubes to glow, if it is on the inner glass surface. Although, that's weird that it's always on one channel even when switching tubes. I've seen oscillation cause blue glow between the plate and the cathode, but not on the glass surface.

Read this link.
http://members.aol.com/larrysb/blue_glow.html

Here is a picture of one of my amps that glow. Sorry for the size

 

[kevinkr]

Differences in the local magnetic fields around the output tubes? Just a thought..

 

[Burnedfingers]

New 6BG6GA's All 6BG6GA's I have are showing some blue glow.

They test and work normally. Besides being SY's favorite tube they just cannot be bad.

How about the way the tube is put together?

 

[SY]

Nice ST-70 there!

 

[m6tt]

As SY's earlier link noted, a lot of tubes where there are holes in the anode glow where electrons 'escape' through these holes. I have some EH 6ca7s which do this and some Sylvania 6ca7s (similar holes in anode) which don't. I'm sure tube construction and the design of the elements can affect this. I like the magnetic field explanation too...Using an old speaker magnet, one can cause the blue electron glow to move etc...