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#272
09-08-2022, 10:25 AM
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It's a bit hard to explain, and remember, this is all founded on educated guess on what MAY be going on in the set.
In normal operation, there is a fair amount of power flowing between the plate and the cathode of a given tube, this causes the plate to heat up, and this heat is felt on the outside glass, if the tube has no power flowing but still has it's heater on, it would be much cooler. And of course, if overloaded, MUCH hotter. https://en.wikipedia.org/wiki/Glowing_plate So, this could also mean that if there was a biasing problem like a H/K short or leak that would prevent the flow of power between the plate and the cathode, or any grid issue, it stands to reason it could be colder than normal. In the same way that a problem causing excessive flow makes it hot. In other words, the radiated power from a H/K short has a much harder time making it to the outside of the tube than an overloaded plate.
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#273
09-08-2022, 10:45 AM
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So even though the tube is not getting super hot it could still pull the voltage down.I forgot to mention the 2nd chroma 6bL8 tube while I had the chassis on the bench and plugged in checking things I noticed this tube had what looked like a blue spot on the side of the tube but once in the cabinet I didn’t see it again.
Last edited by timmy; 09-08-2022 at 11:13 AM.
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#274
09-08-2022, 11:13 AM
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For the case of V6 if it was having an intermittent H-K short (+190v to Y-HEATER/GND) the tube would not heat up very fast, your PWS might give up first, R215 before the tube got really hot, unlike when the audio tube or HOT was overloaded, and all the power was pushed to the plates, and the tubes heated very quickly.
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#276
09-08-2022, 11:24 AM
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a little blue glow is normal, it's just a spot of excitation from being hit from electrons.
I got a picture of a really weird one on a rebuilt CRT i got last year.
__________________
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#279
09-08-2022, 11:37 AM
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https://i.imgur.com/0ykFyqZ.jpg
Blue is not a problem. pink , purple is. https://tonetopics.com/tell-amps-tubes-gone-bad/
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#281
09-08-2022, 12:35 PM
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perhaps what you saw was a bad tube with a purple gassy glow, like seen here,
https://i.imgur.com/z7NnpHg.jpg and not a normal healthy blue glow of a working tube? 
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#282
09-08-2022, 02:22 PM
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I just for giggles tested the audio output tube and it showed grid emission it’s a new tube and didn’t show this when I got it would this be caused from running hot because I’m still not sold on the fact that this tube is supposed to run hot. The volume control is 2 meg I tested it at 2.4 meg.
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#283
09-08-2022, 02:44 PM
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as mentioned. audio output tubes get HOT!
2 alike tubes. https://frank.pocnet.net/sheets/049/6/6AQ5A.pdf 10w max gets up to 250c! http://www.nj7p.org/Tubes/PDFs/Frank/127/6GK6.pdf 17w max no heat listed, but you can bet it also gets over 200c. this is normal
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#285
09-08-2022, 03:03 PM
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Quote:
http://www.tungsol.com/html/faqs3.html
__________________
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