Tube Questions...

[jf5150]

Ok... this is a total newb question... but I come from the EVH school of playing with my ears. I'm a total hack when it comes to technology stuff.

I'm using a Peavey 6505.... sounds great. But, I notice that all four tubes on the back glow orange, but only 3 get blue. Does this mean one of my tubes is out?

thanks guys... sorry for the obvious question haha.

[rockon1]

Swap the tubes around and see if it changes.(put one of the tubes that glows in that socket) If it doesnt its possible that socket has a bad screen grid resistor or something else. Bear in mind not all tube give off fluorescense though and this isnt any sort of conclusive test. It will give you an idea whether something is up with the socket though. Bob

[Amp Kat]

Seen this a bunch in 5150's and it's normal and the amp sounds fine. Just the way it is with these amps but it is normal.

[rockon1]

Seen this a bunch in 5150's and it's normal and the amp sounds fine. Just the way it is with these amps but it is normal.

Might be but it would be difficult to know if one tube was not functioning. Bob

[Amp Kat]

Yeah it would be a good idea to put a bias meter on it and I've done it several times to only be amazed it was pulling just as much as the others and sometimes even more. I can't really explain it and you may be right as it could be out but they never seem to be but it sure looks like it.

[rockon1]

Yeah it would be a good idea to put a bias meter on it and I've done it several times to only be amazed it was pulling just as much as the others and sometimes even more. I can't really explain it and you may be right as it could be out but they never seem to be but it sure looks like it.

Yeah simple bias check would verify things. Bob

[Alex R]

- Connected to the very cold bias in early versions of those amps maybe? A tube opting out of conducting, hence no blue glow?

I note that later versions have bias adjustment on top of the chassis.

[stokes]

Although a blue glow is "normal",not every power tube glows blue.What would concern me is the orange glow you mention.If you are talking about the normal heater glow,that is fine,but if the plates are glowing,there could be a problem.

[TD_Madden]

From http://www.triodeel.com/tubefaq.html

Q. My tubes glow blue when they're on! Is there something the matter?


Usually not. Many large power tubes exhibit some blue glow on the glass, caused by electrons from the cathode flying past the plate (the the large metal structure, aka anode) and hitting residual phosphorous atoms in the glass (how much depends on how much phosphorous there is). All tubes have a small amount of blue glow in the center caused by loose nonreactive gas ions (the fact is that there's no 100% perfect vacuum, so all do this to some extent) such as argon & helium that won't react with the silver stuff ("getter") that's sprayed inside the tube envelope.
Some tubes, such as 0C3 and '83 are GAS tubes, NOT vacuum tubes, and if they don't glow some pretty color (which color depends on the gas used), there's something the matter.


Internal shorts or over-voltages in an amplifier can cause tubes to arc over internally, if you see bright blue glow in a tube after such an occurrence, it's dead.

[rockon1]

Without any further input from the OP further speculation is,well, just that. It would be helpful to know at least if this lack of blue glow follows the socket-better yet to check bias . Bob