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Old 27th April 2008, 01:19 AM   #1
wicked1 is online now wicked1  United States
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Default blue glow on one channel

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!
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Old 27th April 2008, 02:19 AM   #2
SY is offline SY  United States
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http://www.jacmusic.com/html/article...w/blueglow.htm
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Old 27th April 2008, 04:07 AM   #3
wicked1 is online now wicked1  United States
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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!
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Old 27th April 2008, 04:32 AM   #4
m6tt is offline m6tt  United States
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Have you tried replacing the coupling cap? It's a long shot, but I've seen weirder.
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Old 27th April 2008, 05:36 AM   #5
vax9000 is offline vax9000  United States
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Would a high frequency oscillation cause the problem?
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Old 27th April 2008, 05:40 AM   #6
m6tt is offline m6tt  United States
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I've seen weird loading cause blue glows otherwise unexplainable as well. Maybe back emf from a transformer?
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Old 27th April 2008, 05:19 PM   #7
Jeb-D. is offline Jeb-D.  United States
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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
Click the image to open in full size.
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Old 27th April 2008, 11:02 PM   #8
kevinkr is offline kevinkr  United States
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Differences in the local magnetic fields around the output tubes? Just a thought..
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Old 29th April 2008, 12:00 AM   #9
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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?
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Old 29th April 2008, 12:12 AM   #10
SY is offline SY  United States
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Nice ST-70 there!
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