jt1stcav Posted August 1, 2004 Share Posted August 1, 2004 I require the advice from the tube experts here...I've noticed this bluish haze uptop one of my NOS 1940's Delco (RCA) 6J7GTs when the tube is NOT powered up (see the pic above). Normally you can see a blue florescence glow from some output tubes while the tubes are hot and the amp running (chops' KT88s and my 300Bs have that), but this seems different; when the amp's on and the tube's warmed up, the blue haze is NOT apparant, and there's no florescence glow! Strange, eh? EDIT: Correction, when the amp's on and the tube's warmed up, the blue haze is still apparant during daylight hours or if the room's lamps are on, but there's no florescence glow and it doesn't change shape or intesity. If the amp is on or off and I close the blinds and shut off any lamps, the blue ring is NOT visible anymore. Can this be a sign that this tube is gassy and ready to give up the ghost, and go to the big repairman's tube tray up in the sky? Or is it nothing? Brent Jessee said my 6J7GTs are matched up to 4%, reading 106 and 110 transconductance (Gm) on his B&K 747 tester (100 being nominal for brand new tubes). Whaddaya think? All responses greatly appreciated. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 1, 2004 Author Share Posted August 1, 2004 I don't recall the tube having this blue haze before I ever used it; it was as clear as the other 6J7GT is now when I first removed them from their original tube boxes... Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 1, 2004 Author Share Posted August 1, 2004 Uh...yeah, damn cool, I suppose. But that doesn't answer my question, Mark. Do you or anyone else have any clue if this is something to be concerned about? I'd sure hate to have the tube blow while the amp's on and fry its innards or catch on fire (if that's even possible; I really don't want to find out)! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted August 1, 2004 Share Posted August 1, 2004 Only way to know is to have it tested. It may just be discolored glass or something ? Craig Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 1, 2004 Author Share Posted August 1, 2004 And being since it's a NOS tube that hasn't really been used in all these years, it finally shows up now since I've started using it...Hmmm, could that be the answer? Thanks, Craig. Quote Link to comment Share on other sites More sharing options...
Deang Posted August 2, 2004 Share Posted August 2, 2004 If Mark isn't waving the red flags over this I sure wouldn't lose any sleep over it -- especially if things are still sounding good from the channel the amp is driving. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted August 2, 2004 Share Posted August 2, 2004 If it worries you to much send it here and I'll test it for you. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 2, 2004 Author Share Posted August 2, 2004 EDIT: Correction, when the amp's on and the tube's warmed up, the blue haze is still apparant during daylight hours or if the room's lamps are on, but there's no florescence glow and it doesn't change shape or intesity. If the amp is on or off and I close the blinds and shut off any lamps, the blue ring is NOT visible anymore. Dean, thanks for the reply...there's no change in the right channel, and when switched to the left, still no change in the sound (so far). Mark, sorry for being an ***! I was just frustrated when I got your response is all. Dean's right, if it was something major, you'd have told me beforehand. Craig, I just may take you up on your offer...thanks! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted August 2, 2004 Share Posted August 2, 2004 I'm pretty sure from your Edit that the glass is just discolored. But the offer stands. Quote Link to comment Share on other sites More sharing options...
Cal Blacksmith Posted August 2, 2004 Share Posted August 2, 2004 I don't want to sound like an A$$ but are you sure it is not a refelection from somewhere in the room? It is not comming from inside the tube, and if you shut off light sources to the room, it is gone, it sure sounds like a refelection to me. Have you shielded the tube with your hands while the lights are on to see if you can get it to go away? What do I know? I am just looking at it in a picture. Nevermind if I am wrong! Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 2, 2004 Author Share Posted August 2, 2004 That's cool...I appreciate your response (and you're not an ***). I pulled the tube out and held it in my hands away from the amp, and that blue discoloration is still there on that one particular tube, so no, it's not any reflection. And it's not on the outside glass that you can simply wipe away...it's definately inside the tube between the element and the inside wall of the glass. If there was a room reflection somewhere that caused that haze to appear, I'd assume you'd see it on every tube in my room, not just one single tube. Plus I just switched tubes (the discolored 6J7GT is now at the left channel and the clear 6J7GT on the right). Yep, you guessed it...the hazey blue tube is still visible while the amp's off. I'm playing my system right now, listening to a home-brew CD-R of a live digital recording of a friend's residence 1927 WurliTzer theatre pipe organ, and there's absolutely no difference in sound or channel imbalance. My amp's working flawlessly, and eventhough the discolored driver is now on the left, its appearance hasn't changed one bit. Aside from the normal orange glow inside the anode, the blue ring is also quite visible. I wonder how often something like comes along? If I had kept the stock Russian metal 6K7s in place and one of them developed this blue haze inside its glass, I'd be none the wiser for I wouldn't be able to see it! Quote Link to comment Share on other sites More sharing options...
artto Posted August 2, 2004 Share Posted August 2, 2004 ---------------- On 8/2/2004 7:04:03 AM NOSValves wrote: If it worries you to much send it here and I'll test it for you. ---------------- What?! Don't they have those "tube testers" at the drug store anymore? Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 2, 2004 Author Share Posted August 2, 2004 Man, do I wish they did! Those days are long gone... Quote Link to comment Share on other sites More sharing options...
mike stehr Posted August 2, 2004 Share Posted August 2, 2004 Carbon buildup? Quote Link to comment Share on other sites More sharing options...
bkrop Posted August 2, 2004 Share Posted August 2, 2004 1) Does it smell bad when you are standing near it? J/K 2) Maybe your bro is messing with you using a magic marker/highlighter! Quote Link to comment Share on other sites More sharing options...
edwinr Posted August 2, 2004 Share Posted August 2, 2004 That's a strange one. Maybe it's a slight imperfection in the glass tube itself, as it warms up the glass discoloration shifts color frequency and then you can't see it. I think I know what I mean - but I'm having trouble trying to say it! Quote Link to comment Share on other sites More sharing options...
neo33 Posted August 2, 2004 Share Posted August 2, 2004 I think I know what you mean, too. . Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 2, 2004 Author Share Posted August 2, 2004 ---------------- On 8/2/2004 7:58:40 PM edwinr wrote: That's a strange one. Maybe it's a slight imperfection in the glass tube itself, as it warms up the glass discoloration shifts color frequency and then you can't see it. I think I know what I mean - but I'm having trouble trying to say it! ---------------- I'm not sure I know what you mean, edwinr. The only time I can't see the haze is when the it's dark in the room. My desk lamp is on low setting above my computer, and as I walk up to the amp to gaze at the infected tube, I can't see the haze at all! But I know it's still there...when I turn on the ceiling fan lamp, it's still there in all its hazy glory (ugh)! But you're right, though...that's a strange one alright! Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted August 2, 2004 Author Share Posted August 2, 2004 It doesn't smell bad, but it does stink if you know what I mean. And chops knows better than to mess with his older brother! Carbon? Could be... Quote Link to comment Share on other sites More sharing options...
radiob Posted August 7, 2004 Share Posted August 7, 2004 Play some Jimmy Hendrix Purple Haze, kick back and watch to see if the color changes from blue to purple. Quote Link to comment Share on other sites More sharing options...
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