Rickresource Rickenbacker Forum

Greg: I have often read that the blue glow in tubes, most often power tubes, is quite normal. My question is, are there different types of blue glow. I have recently seen an uncharacteristic blue glow, almost ghostly like, that covers most of a 6L6, Electro Harmonix. Not just a localized area, but moving about throughout most of the tube. Your comments would be appreciated.

Peter, the correct term is called Blueglo!

So long as it doesn't turn into FireGlo...

I don't know the answer I'm afraid but I'm interested to know if, where you say "moving about throughout most of the tube" you mean it's in constant motion or does it expand to fill it and then doesn't change. Does the intensity change when the valve is driven harder?

My understanding of the blue glow is that the tube was not totally evacuated when sealed. 6L6 tubes seem to have the blue glow occur more than other power tubes.

This is taken from Kevin O'Connor's FAQ on his London Power site. It answers the question about blue glow quite well. If anyone has never seen his site or his books, and they want to learn more about tube amps, they are missing out. I encourage anyone who has moderate knowledge about how tube amps work and who would like to learn more to visit his site and check out his books. If you're not so knowledgeable, and still want to learn, then read his FAQ and post a question on a seperate thread and I can recommend some better books for beginners.

http://www.londonpower.com/faq.htm

Q: What does it mean when my power tubes glow blue? Should I toss them?

A: No, you don't have to toss them just yet. However, a blue glow indicates the presence of some gas in the tube, which is not a problem in most situations. If you have noticed an increase in the amount of blue, then you might want to get a new set of tubes sooner than later. Too much gas in the tube can lead to bias failures, blown fuses, and possibly blown output transformers.

WARNING!

If your tubes are glowing bright orange - that is, the grey parts inside the tube are glowing orange - TURN THE POWER OFF IMMEDIATELY! A bias failure is in progress. Usually, this is the fault of the tube itself, but can also be caused by an open grid resistor, bad socket connection, or poor solder connection. Check the bias voltage right on the tube socket with no tube plugged in. If the bias is okay, plug in a new tube.

Maybe Paul can do a Blue-Orange burst called Nobiasglo!

Thanks, Greg.

jps wrote:Maybe Paul can do a Blue-Orange burst called Nobiasglo!

Every-body's a comedian!

I've seen 6L6's glow blue for years and function fine.

I have an original 1963 Brown Face Blonde Fender Twin on which the innermost power tube does a bit of blue glow when the vibrato is turned on.

johnallg wrote:My understanding of the blue glow is that the tube was not totally evacuated when sealed. 6L6 tubes seem to have the blue glow occur more than other power tubes.

That's true to an extent, as there is no such thing as a perfect vacuum and there's some slight ammount of air left in a tube when sealed.That's taken care of by an item in the tube called a getter, which gets flashed, and consumes the remnant air.That's what causes the silver blotch spot on the glass.

When I was a kid I would enjoy watching the 6L6s in my showman glow blue/purple . They kinda flashed around while I played bass through them . Mmmmm maybe I was tripin a little . If they got real blue they would start to sound mushy and I would replace them with nice new ones that would glow............Blue !

I have only rarely seen 6550's glow blue and even then only a faint glow near the base. 6L6's seems to do it a lot.

VRICKY63 wrote:When I was a kid I would enjoy watching the 6L6s in my showman glow blue/purple . They kinda flashed around while I played bass through them . Mmmmm maybe I was tripin a little . If they got real blue they would start to sound mushy and I would replace them with nice new ones that would glow............Blue !

Hmmm....I'll have to turn the head around the next time I turn it on

Yes, there is something about Fenders with blue 6L6's that brings me back, also Silvertone twin twelves with blue 6L6's, come to think of it anything with 6L6's.