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Orange glowing EL84?


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My understanding is SPECIALLY RATED vacuum tubes are supposed to run when red, orange, or white hot; but most normal vacuum tubes should exhibit a blue glow when warmed up.

 

... I believe I'm looking at the EL84, I think; it's the tube that's not in the metal cylinder in the Valve Junior Combo (on the left, looking in the screen from the back). I haven't opened it and can't see the logo; the design looks like a Sovtek from pictures of like every kind of tube I can find (Wikipedia for EL84, they have a gallery).

 

... AND IT'S GLOWING ORANGE. That's hotter than red, and that's after a 10 minute warm-up period. I can feel an... awful damn lot of heat coming off the back of my amp if I get close to the screen too. I mean, it's a small heat source, but it's like a tiny space heater.

 

Is this wrong? Someone mentioned the amp runs the EL84 "a little hot," but it's up two color phases higher than I thought tubes were supposed to run at!

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The heater filament will normally glow orange or yellow, just like a low wattage light bulb, which it is!

 

It the plates start to exhibit a stripe of red or orange glow, your tubes dissipating too much power and red plating.

 

According to the Groove Tubes guy, Aspen Pittman, who wrote about it in his Tube Amp Book, the blue glow is just fluorescence from a poor vacuum in the tube. A little glow around the base is fine, but the more blue glow you have, the lower the vacuum and the faster the tubes will die; yet, they do tend to sound sweeter than tubes that glow less.

 

Enjoy it while they last!

 

Gil...

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the blue glow is just fluorescence from a poor vacuum in the tube. A little glow around the base is fine' date=' but the more blue glow you have, the lower the vacuum and the faster the tubes will die[/quote']

 

I was under the impression the whole plate was supposed to glow blue, but if it glows purple it's oxidizing due to gas in the tube and thus will die soon. The tubes heat up a cathode that then releases electrons (excited electrons, extra energy, energy comes from heat, etc) which then move towards the colder anode due to thermodynamics and charge.

 

I also read some tubes are made to run glowing red, orange, or even white hot; but most shouldn't, and only special circuits require these types of tubes.

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