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Blue glow

whoaru99

whoaru99

Epic Member
A recent question about blue glow got me thinking about something.

My previous tube amp used the same power tubes, OPTs, and PT as my current amp. Not just same type, but THE actual same parts. All those parts were re-purposed into this new amp.

The new amp uses SS rectifier so B+ is higher than tube rectified in prior version and the tubes are biased roughly the same as before 40mA vs 42mA or so.

This new amp is fixed bias, the previous version was cathode bias.

The new amp, a bit to my disappointment, has almost no blue glow on any power tube while the previous version had quite noticeable blue glow on all the power tubes.

Any thoughts why that may be?
 
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Have a general understanding of what it is.

Looking for thoughts or speculations why the two amps would be so different in amount of blue glow, considering post #1 info,
 
Could be different plate and screen voltages (ratio) or damned near anything else. It's nothing really to worry about.
 
I'm not worried, I'm somewhat disappointed.

The amp sounds great, better than before, but I miss the blue glow.
 
Using the same brand of tubes? Maybe some do and some don't. Or this one won't do it but her sister will.

I got nothin' really. :D
 
The exact same set of tubes I was using in the other amp. Not a new or different set of the same type...they're the tubes I had been using in the other amp.
 
I'll go with lower voltages. Seems that hot screen supplies really make things glow. Makes the screens glow orange too if you crank the amp, which is not exactly the friendliest thing on the tubes.
 
Well, B+ is higher now that it was in the old amp. The old amp I had run pentode, triode, and UL at various times and didn't notice much difference in blue glow. It's hardwired UL at present.

I may try increasing bias by 5 or 10mA per tube just to see if anything happens with the blue glow. They're (the "super" 6BG6GA tubes) a little on the cool side now at 40mA (400-410V on the plates, fixed bias), aren't they?
 
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math says 16.4ish watts dissapation. should be able to run those hotter without issues. Try about 50 ma and see what you get.
 
Blue glow is fun but not always predictable. I'd like to think this NOS 807 was just letting me know how it felt to have some voltage applied to it after a 65 year slumber in its original packaging.

 
In my experience you only get a decent blue glow when your tubes have big holes in the side of the plates. If the plates lack these holes, then its hard for the glow to make its way to the glass.
 
Somebody should bottle this stuff, slap an AK logo on it and sell it as an AK fundraiser. Blue Glow Spray. Spritz your tubes every 20 hours of operation for best effect. Spritz when they're cold, of course!
 
goldear said:
In my experience you only get a decent blue glow when your tubes have big holes in the side of the plates. If the plates lack these holes, then its hard for the glow to make its way to the glass.
Click to expand...

No holes on the sides of the plates, yet the exact same tubes running off much of the same amp content, had blue glow before.

It's a real head-scratcher.
 
The blue glow in my power tubes is drawn towards the side of the bottle nearest the power trsnsformer. Perhaps use a magnet to try and coax them out of hiding, you know they're in there. Also, jack up that bias to 50ma and report back.
 
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I just use a blue LED.
 
Scuzzer said:
Blue glow is fun but not always predictable. I'd like to think this NOS 807 was just letting me know how it felt to have some voltage applied to it after a 65 year slumber in its original packaging.

Click to expand...

:D HaHa.. Big smiley face with horns...you see it right:scratch2:
 
My Latino St-120 amp had the "Blue Glow" on all 4 KT88 tubes. Really cool to look at. In fact, I just got it running again after I blew a tube and melted some resistors. Listening to it now :music: I'll have to wait until night time to see if the Blue comes back.
 
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