What does it mean when one tube glows blue?

[Xqzdust]

boogiemon wrote:
re-bias? i thought boogies are fixed-bias...



They are fixed bias, but you they can be adjusted slightly (or so I believed, someone correct me if i'm wrong).

Fixed bias refers to the amp having a fixed resistor instead of a bias pot that ,of course, would be adjustable by turning it like a volume pot.
With a fixed bias you can adjust the bias by changing the bias resistor to one with a different resistance value. Far more complicated but, then again, Randall doesn't want you changing the bias on his amps does he?

 

[tony777]

Randall doesn't want you changing the bias on his amps does he?

The whole idea is based on maintenance free operations since any tube tech used to say you need to adjust the amps bias and achieve easy money. With mesa amps' fixed bias, you just swap tubes. Easy and you can swap tubes in a minute when you want to try out something else.

 

[Xqzdust]

Tony777 wrote:

The whole idea is based on maintenance free operations since any tube tech used to say you need to adjust the amps bias and achieve easy money. With mesa amps' fixed bias, you just swap tubes. Easy and you can swap tubes in a minute when you want to try out something else.

Quite true! I once had a store tell me that my tubes would not have any warranty if I didn't pay for their tech to check and re-bias my amp. That old Music Man still hasn't been re-tubed! My post was meant to explain what "fixed bias" really means. Maybe the term should be "really hard to adjust bias" or perhaps "bias you shouldn't mess with"! I stand by my statement: Randall doesn't want you to fool with the bias on his amps. He wants you to buy tubes from him. I do feel that it is a much simpler way for the amp owner and more profitable for Mesa! Not saying it's wrong, It's just the way it is.

 

[boogiemon]

...Still haven't had the chance to turn it up, but the clean channel sounds good now & also when i look in the back, *both* tubes have a blue glow.

...Just got a call from the factory and the answer in this case is that the left tube socket had a loose/broken ground connection. I'll get it back tomorrow or next week and post again on what sonic difference there is if any.

It's a sixty-watter: only two power tubes. The position on the right (looking from the back) glows blue which I know is ok, but shouldn't both positions do this? I've tried swapping tubes but it's always the one on the right that glows blue.

When working the tubes should always glow blue.

If running in Simul class all 4 should glow, in Class A the two outer ones only should glow.

If the tube that isnt glowing is selected then it may be defective. How old are they and what kind are you using?

 

[fretout]

IIRC, if a tube glows blue, it means that some oxygen has made it's way inside the tube...

I have noticed that the inner 2 tubes in my Mark IV glow blue, while the outer pair are just fine (orange glow).

 

[boogiemon]

i'm no expert, but i don't think that's true. The silver stuff inside tubes is called beryl i think & it's there to bind to any oxygen that might get into the tube.. If your m4 is running all 6l6's, try swapping the inner pair w/the outer pair & i'll bet that it's still the inner pair that glows blue.

IIRC, if a tube glows blue, it means that some oxygen has made it's way inside the tube...

I have noticed that the inner 2 tubes in my Mark IV glow blue, while the outer pair are just fine (orange glow).

 

[av8or3]

Any orange glow you see from 6l6's would be the heater. When the tube is working the blue/violet glow you see is the cloud of electrons that are moving about. A blue glow in a tube is a good thing. El84'S do it,El34's do it,6l6's do it and 6v6's do it too. (although on the "grey" 6V6's you can't see through the darkened glass)
I completely understand why the tube you had wasn't glowing because of a socket problem. I'll bet you're in for a pleasant surprise when you get your amp back, it's got to have more power/headroom since one of the power tubes that wasn't working now is.
If you look hard enough, there will always be a blue/violet glow coming from inside the plates on power tube. Some are brighter than others, but all should have some.
Jim

 

[boogiemon]

Yeah, it's a little monster once again.

Any orange glow you see from 6l6's would be the heater. When the tube is working the blue/violet glow you see is the cloud of electrons that are moving about. A blue glow in a tube is a good thing. El84'S do it,El34's do it,6l6's do it and 6v6's do it too. (although on the "grey" 6V6's you can't see through the darkened glass)
I completely understand why the tube you had wasn't glowing because of a socket problem. I'll bet you're in for a pleasant surprise when you get your amp back, it's got to have more power/headroom since one of the power tubes that wasn't working now is.
If you look hard enough, there will always be a blue/violet glow coming from inside the plates on power tube. Some are brighter than others, but all should have some.
Jim