Hi,
I just bought a couple of WE 300b's for my monoblocks. I urgently opened the nice blue boxes and installed them in my amps, replacing a pair of Svetlana 300b's.
I turned the power on and both tubes have the blue corona at the top of the glass.
I did a search here and found out, ( I hope), that this is normal for new tubes and will/should lessen as the getters do thier job and eliminate most of the gas molocules left from the construction process.
I quess I just want to be reasured that I not damaging the most expensive tubes I have ever payed my hard earned cash for.
There is no blue glow inside the filament area, just at the tops and it does look cool.
I just bought a couple of WE 300b's for my monoblocks. I urgently opened the nice blue boxes and installed them in my amps, replacing a pair of Svetlana 300b's.
I turned the power on and both tubes have the blue corona at the top of the glass.
I did a search here and found out, ( I hope), that this is normal for new tubes and will/should lessen as the getters do thier job and eliminate most of the gas molocules left from the construction process.
I quess I just want to be reasured that I not damaging the most expensive tubes I have ever payed my hard earned cash for.
There is no blue glow inside the filament area, just at the tops and it does look cool.
Hi maybeim;
I agree with GabeV FWIW. Your description is consistent with excitation of phosphorescent materials in or on the glass envelope rather than excitation of stray gas molecules. If it is a gassey valve, you will see a diffuse blue glow with no sharply defined borders that is in the space INSIDE the glass envelope. If it is just electron excitation of phosphors on the glass, the blue glow will ONLY appear on the inside surface of the glass (and also possibly on the inside surface of the plate structure for the same reason).
Good luck and all the best,
Morse
I agree with GabeV FWIW. Your description is consistent with excitation of phosphorescent materials in or on the glass envelope rather than excitation of stray gas molecules. If it is a gassey valve, you will see a diffuse blue glow with no sharply defined borders that is in the space INSIDE the glass envelope. If it is just electron excitation of phosphors on the glass, the blue glow will ONLY appear on the inside surface of the glass (and also possibly on the inside surface of the plate structure for the same reason).
Good luck and all the best,
Morse
I have some 6V6EH that have been used for a year or so, and have a blue glow, it is entirely normal. They have not changed much since they were new. If you look closely, it is definitely the glass that is fluorescing. (I guess due to secondary electron emission? Bonus question for the physicists! 
) The central plate/grid/cathode structure has no glow around it.
I think part of the reason that old tubes are so often coated with grey or black paint inside is to remove this glow, so people wouldn't think the tubes were gassy...
As an aside, I found a tube the other day with a bubble in the glass! Is this likely to fail? I already broke the "outside" of the bubble, guess I should be more careful...
) The central plate/grid/cathode structure has no glow around it. I think part of the reason that old tubes are so often coated with grey or black paint inside is to remove this glow, so people wouldn't think the tubes were gassy...
As an aside, I found a tube the other day with a bubble in the glass! Is this likely to fail? I already broke the "outside" of the bubble, guess I should be more careful...
In fact, blue glow on the glass is a sign of a *good* vacuum, showing that the electrons survived the trip without hitting any gas. A common tube that does a lot of blue is the 6L6.
Now, one thing that I was wondering, inside a Russian 6P3C-E (6L6 equiv.), at 25W Pd (just a little over ratings, but it's a husky tube), 330Vp, the plate *coating* (not the plate itself) glows red (incandescent), and has a bit of blue fluorescence too. Is this normal? I think it is, since all the 12AU7s in Hept'AU7 do it (a very small band, visible at exactly two angles, but definetly on the plate). (They have a similar grey plate.)
Tim
Now, one thing that I was wondering, inside a Russian 6P3C-E (6L6 equiv.), at 25W Pd (just a little over ratings, but it's a husky tube), 330Vp, the plate *coating* (not the plate itself) glows red (incandescent), and has a bit of blue fluorescence too. Is this normal? I think it is, since all the 12AU7s in Hept'AU7 do it (a very small band, visible at exactly two angles, but definetly on the plate). (They have a similar grey plate.)
Tim
Hi Bas,
I edited then saw your post. I wasn't sure if he'd find it funny, although I'm chuckling in memory of one of the best ever threads on "tubes".
Perhaps we can gang up and ask "what the best 12A_7 tubes are to blend your mind into the aural matrix and become one with the harmonic infrastructure of the music?"
I edited then saw your post. I wasn't sure if he'd find it funny, although I'm chuckling in memory of one of the best ever threads on "tubes".
Perhaps we can gang up and ask "what the best 12A_7 tubes are to blend your mind into the aural matrix and become one with the harmonic infrastructure of the music?"
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