One tube with blue light

[feeench]

Recently got my S.E.X. 2.1 built, had a hum in both tubes at first which totally subsided in one tube but I still have a faint hum in the other. It's heater cathode leakage. The amp hasn't been shut off at all for the past ~100hrs (except to install the C4S ). I can't hear the hum with my speakers anymore but I can still easily pick it up on my HD650's. I have new tubes coming but I just wanted to ask about the blue light...

Here's a pic of the good tube:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FyXcerDLl.jpg&hash=6f98919deda0eca69fbf0162c142efea88495a8d)

And the tube that hums:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FBhRoNuWl.jpg&hash=bcb076c289743ac26a3d768d1468f55d54645930)

Should I be worried? I heard a pop from my speaker hooked to the bad tube earlier which was the first time I heard it do that.

Should I wait until I get the tube replaced before running the amp? TIA!

[Paul Joppa]

That picture looks like there's some gas in the tube. Normally the getter will eat the gas, though if it hasn't done so in 100 hours, I'd replace the tube. Can you see the getter flash?

Good reference: http://www.thetubestore.com/Resources/Matching-and-other-tube-info/Blue-Glow

[feeench]

Hey Paul,

Yeah I see the getter flash, both tubes look almost exactly the same from my eyes, the bad tube may have a bit more of a rainbow effect around the edges of the flash (we're talking about the silver/grey coating on the glass, right?) but it's a very minor difference.

Another thing I noticed is the heater filament on the bad tube looks strange to me... If I look really closely from the top so I can see the whole filament through the bigger section, it kind of bulges out at about the half way point towards the getter side of the tube. The other one is flat against the one "wall" inside there which is how I reckon it should be... Maybe this is the source of my humming... *shrugs* I'm pretty new to this!

At any rate I have 1 Sylvania replacement tube along with a pair of GE's in the mail. I read through that link you posted (thanks) and it sounds like I'm okay to run the amp in the mean time... I've definitely got over 100hours on the tubes so I'll probably be trashing the bad tube.

Cheers


EDIT: The hum in the bad tube has gone now, well after 100 hours. I've heat cycled the tubes a few times tonight, maybe that has something to do with it? I still have the blue glow, however.

EDIT2: I take it back. The hum is back. *shrugs*

[Paul Birkeland]

If the hum has gone from constant to intermittent, you may indeed be close to the point where it may cook off for good.  The getter should indeed eat that up, but it shouldn't take all that long. 

[feeench]

Hum has been gone for a day now, cool!

The blue light has subsided a bit but is still there.

Sounds great now.