Hey all. Another blue glow question:
I have a VHT pittbull UL, that uses 4 KT88's. I had 4 new tubes installed about 3 months ago(Sovtek, all 4 matched) by a local professional luthier.
Normally, all 4 of my tubes have a nice subtle blue glow when standby is off.
I noticed recently that one of the tubes does not have that blue glow anymore when standby is off - I trued moving the tubes around, and sure enough, the same tube does not glow, but the others do.
I contacted the dealer I got them from (tubestore), and they said it's nothing to worry about unless I noticed a big difference in sound, which I'm fairly sure there is no difference. I'm wondering if I should return the tubes for testing/replacement under warranty just in case.
What do you all think?
I have a VHT pittbull UL, that uses 4 KT88's. I had 4 new tubes installed about 3 months ago(Sovtek, all 4 matched) by a local professional luthier.
Normally, all 4 of my tubes have a nice subtle blue glow when standby is off.
I noticed recently that one of the tubes does not have that blue glow anymore when standby is off - I trued moving the tubes around, and sure enough, the same tube does not glow, but the others do.
I contacted the dealer I got them from (tubestore), and they said it's nothing to worry about unless I noticed a big difference in sound, which I'm fairly sure there is no difference. I'm wondering if I should return the tubes for testing/replacement under warranty just in case.
What do you all think?
It is fine. The inside of the bulb was probably cleaner than the others. A bright blue glow often means the input grid capacitor is leaking DC and should be replaced. The lack of glow could mean low or no emission and that you could notice.
So the inside somehow got cleaner is what you are suggesting? Like I said, the last 2.8 months the tubes have all had the exact same glow, now suddenly, one does not, regardless of where I move it...?
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Blue Glow in Electron tubes
Unless the glow is inside the tube elements, you shouldn't worry too much...
Unless the glow is inside the tube elements, you shouldn't worry too much...
This blue glow is caused by cobalt contamination. The cobalt ions fluoresce when hit by stray electrons. Seen the same thing myself. The RCA 807s glowed prettily when they were new. Over time, the glow has lessened considerably. It's only an aesthetic detriment.
Other RCA tubes (6AQ5s) also started out with that blue glow that has almost completely disappeared.
On just about any material produced the start and end of the run are a bit different from the middle of the batch. Even when formed in laddles the sides of the product are different. So one tube stopped glowing first, only a cosmetic issue.
If you're really worried about it, you can check the cathode current of each tube to see if they're all in the same ballpark....all should be within a few mA.
Alright I see that it is normal for this to happen. But why just this one tube? why suddenly? One day, it had the exact same glow, the next, no glow at all. I did even more 'cosmetic' testing and had the amp in standby in a pitch black room(night time no lights on) and took standby off, and the other three tubes all glowed nicely, while the problem tube still had 0% blue glow. It just seems odd that tubes that normally glow blue, just suddenly stop.
To me, no one has explained why it stopped glowing blue, only showing links and explaining WHY they glow blue(or dont). Don't get me wrong, these are all great answers, but still don't answer my question. Thanks for the help!
To me, no one has explained why it stopped glowing blue, only showing links and explaining WHY they glow blue(or dont). Don't get me wrong, these are all great answers, but still don't answer my question. Thanks for the help!
That is a really good question, but since people don't even agree on exactly what causes the blue glow other than energy hitting substances it seems an accurate answer would require real work.
If however you want a soothing inaccurate answer it is because there was less contamination and the gettter finally absorbed all of it. Or the tube was bumped slightly and fewer electrons escape or the cathode emission fell off just enough to stop making the glow.
Thank you simon, I understand. I did more sound testing, and came to the conclusion that there is no change in the sound in my setup. I'll just have to deal with 3 pretty tubes and one ugly one 🙂
I'm wondering now, if anyone else has had similar problems(maybe now, NOT a problem but 'event') happen to their tubes?
I'm wondering now, if anyone else has had similar problems(maybe now, NOT a problem but 'event') happen to their tubes?
My GU-50 glowed blue initially too... and so did my 4P1L... but as they were used the getter changed colour and the blue glow disappeared...
The blue glow going away shows that you have a working getter... a good sign... I am sure the blue of the other tubes will eventually fade over time too... if you really want some blue glow, perhaps you could mount some small blue leds below the sockets of the tubes and let these light up during use like some of the"tacky" looking Chinese amps....
To me this is purely cosmetics and I think at the end of the day, I would prefer good sounding tubes rather than good looking ones.. although perhaps having both would be best... 😀😀
The blue glow going away shows that you have a working getter... a good sign... I am sure the blue of the other tubes will eventually fade over time too... if you really want some blue glow, perhaps you could mount some small blue leds below the sockets of the tubes and let these light up during use like some of the"tacky" looking Chinese amps....
To me this is purely cosmetics and I think at the end of the day, I would prefer good sounding tubes rather than good looking ones.. although perhaps having both would be best... 😀😀
In my set of 6551's I once had too much bias, they glowed, and I reduced until no visible effect. I reduced from some 50 mA to 45 mA.
Same with my DHT triode, 10Y. These were old so I took it more as a sign of too high a voltage/bias, and reduced the HV as well (from 400 to 380 @ 20 mA).
Also in a Russian tube that I bought for replacedment for 6L6 in my nephews' amp, I saw that glow. Again here the effect had to do with the bias/voltage. The tube had a lower max power, I thought that the root cause.
Have a look at tghis page describing the phenomenon in a different way: Blue Glow.
This website thinks it is harmful, gassy origins...
Anyway nice pictures...
I suspect that they would be contributing to sound and background noise, scintillating is a word to convey something we here isn't it.
Same with my DHT triode, 10Y. These were old so I took it more as a sign of too high a voltage/bias, and reduced the HV as well (from 400 to 380 @ 20 mA).
Also in a Russian tube that I bought for replacedment for 6L6 in my nephews' amp, I saw that glow. Again here the effect had to do with the bias/voltage. The tube had a lower max power, I thought that the root cause.
Have a look at tghis page describing the phenomenon in a different way: Blue Glow.
This website thinks it is harmful, gassy origins...
Anyway nice pictures...
I suspect that they would be contributing to sound and background noise, scintillating is a word to convey something we here isn't it.
For reference, blue glow has been discussed here:
http://www.diyaudio.com/forums/tubes-valves/162947-blue-glow-how.html
There are difference kinds. Some normal, some bad.
http://www.diyaudio.com/forums/tubes-valves/162947-blue-glow-how.html
There are difference kinds. Some normal, some bad.
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