tube color when warm turns Blue (SOLVED) - Printable Version

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+--- Thread: tube color when warm turns Blue (SOLVED) (/showthread.php?tid=16648)

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tube color when warm turns Blue (SOLVED) - jcassity - 05-13-2017

I have a 6k6GT that when i turn my radio on, it emits a sorta neon looking blue color.

the 6k6's are different brands.
i have the original totally blacked out philco 6k6's which are good put back as spare.

 I have 220degF on one 6k6, i have 245degF on the one that goes blue looking.

i moved the two 6k6's and it is infact the tube turning blue and not something about the circuit feeding it.

is this ok?

if so, how do i get more of these tubes that go blue?  looks really nice

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RE: tube color when warm turns Blue - Mondial - 05-13-2017

The blue tube is probably gassy and no good if the blue glow fills the space inside the tube. That means air has leaked inside and contaminated the vacuum. The fact that the blue tube is getting hotter is not a good sign.

If the blue glow is on part of the inside of the glass surface only and not filling the space then it is just harmless florescence caused by stray electrons hitting the glass.

If there is any doubt, replace the blue tube because a gassy one can go into a runaway condition where the current keeps rising until something eventually burns up.

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RE: tube color when warm turns Blue - jcassity - 05-13-2017

its blue along the exterior of the glass, not in the central areas where the orange glow is happening.

its like a halo of blue so to speak ...

what say you?

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RE: tube color when warm turns Blue - Mondial - 05-13-2017

If its only along the surface of the glass then its probably ok. If you have a glow around the actual tube elements then that's a problem.

I would still monitor the temperature of the tube and make sure it does not keep increasing after its been on for a while.

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RE: tube color when warm turns Blue - jcassity - 05-13-2017

thanks,, this is a new old stock tube i got from Gary up in ohio,,
i will order another.
I dont want to use my original Philco tubes ,, all of them were good except 1 and would like to save them back as spares.

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RE: tube color when warm turns Blue (SOLVED) - codefox1 - 05-13-2017

Sometimes the flourescence will "dance" to the music in an audio amp. As stated, if it's probably gassy, even NOS tubes can get this way. I've heard about running 'em for a while can sometimes clear up some gas to the degree possiible with the internal getter. I can recall an ancient Eico that did this. The 6L6's lasted for years!

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RE: tube color when warm turns Blue (SOLVED) - jcassity - 05-13-2017

here is a picture of the tube
two 6k6's side by side from left to right.

to the far right is my rectifier tube

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