Blue glow in tubes... uh-oh?

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timthetortoise

MADE OF SANDALWOOD
So, I've read the various FAQs on blue glow in tubes, and when I started seeing it in my tubes I didn't think anything of it. However, tonight I looked a bit closer and noticed that the glow is situated visibly in two main areas. It looks like it may be in a bad place, but the tubes still sound okay. The blue started after I biased the amp (following instructions from section 2 of this document), but I only measured voltage on socket 1 instead of both 1 and 4. My camera decided to crap out, but here is a photoshopped picture of the tube + locations of glow.
https://i5.photobucket.com/albums/y196/xtjdx/blueglow.jpg
Is this something I should be worrying about? I plan on rechecking for bias creep next time I'm with the amp, but should I bring up my older set of tubes just in case? I'm deathly afraid that one of the tubes is going to blow and cause a total meltdown of this amp, something I definitely can't afford. :mad:
 
It means that some gasses have found their way into the tube. This can come from several sources. A microscopic leak can allow air into the tube. Another source is "outgassing" from the cathode, which is heated to "boil off "
electrons. There is a tiny amount of mercury placed within the envelope which is called "getter" and its function is to capture and bind any gas molecules that may float by. Hazard?? Not really. I have played gassy tubes for years without incident. Your local music store may disagree, but they want to sell you a new set of tubes. In my experience, there is moredanger in setting a beer on your amp than from gassy tubes.


chazba
 
Yeah, that's what I figured, but I remember reading somewhere that fluorescence between components can be a sign of damage elsewhere. Probably just more mythology. Thanks for the clarification.
 
chazba said:
It means that some gasses have found their way into the tube. This can come from several sources. A microscopic leak can allow air into the tube. Another source is "outgassing" from the cathode, which is heated to "boil off "
electrons. There is a tiny amount of mercury placed within the envelope which is called "getter" and its function is to capture and bind any gas molecules that may float by. Hazard?? Not really. I have played gassy tubes for years without incident. Your local music store may disagree, but they want to sell you a new set of tubes. In my experience, there is moredanger in setting a beer on your amp than from gassy tubes.


chazba
Click to expand...


Totally agree....I played my old 50 watt Fender amp for years with that kookey, eerie blue look!! (they were once completely orange!!).
All safe! Still sounded good!...until my then girlfriend poured/spilt a Bicardi down the back of it, accidentally, I think.
 
Not an expert but IMHO don't sweat the blue. Bright orange/red, you got problems but blue OK.
 
Yeah on the Orange/red color. That means that there is excessive plate current, possibly caused by changes in the bias circuit, or the control grid being dislocated, permitting more current to flow in the plate circuit (Ip). Swap out the tubes and if it continues, take the amp to your friendly local tube geek. If you fail to correct the problem quickly you may damage the power supply components or possibly the output transformer. Either one will be a major expense, especially in vintage gear where parts are difficult to locate and very expensive.

chazba
 
Back in the day, I knew a guy who put a Formica top on his amp because he always had a drink and an ashtray on it at the gigs. No Shit!!!


chazba
 
chazba said:
Back in the day, I knew a guy who put a Formica top on his amp because he always had a drink and an ashtray on it at the gigs. No Shit!!!


chazba
Click to expand...

A friend of mine was playing a gig with his brand new Laney amp with vents on top. He set a drink on top of the amp next to a vent. You know where this is going, don't you?

He had a banner with his band's name on it duct taped to the wall behind the stage. The duct tape gave way, the banner fell onto his amp, and dumped his icy full drink right down one of the vents. A cloud of steam erupted from the vent and the amp made a very bad, very loud, very short noise and shut down. Every tube was shattered, but luckily for him, replacing the tubes and a massive cleanup restored the amp. He doesn't put drinks on his amp any more, though.
 
Ooops! I get a little testy when fellow jammers use my rig as a coaster.
 
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