When I run my head at any volume over 2, the tubes glow a normal orange in the middle, but glow blue at the top and bottom. Is this normal or are my tubes bad?

Edit: Image

Fender Strat
Epi Joe Pass Signature
Epi LP Plus Top
Jackson Dinky
Fender Hot Rod Deville 212
Last edited by Rio38 at Dec 30, 2009,

C. Blue Glow -- what causes it?

Glass tubes have visible glow inside them. Most audio types use oxide-coated cathodes, which glow a cheery warm orange color. And thoriated-filament tubes, such as the SV811 and SV572 triodes, show both a white-hot glow from their filaments and (in some amplifiers) a slight orange glow from their plates. All of these are normal effects. Some newcomers to the tube-audio world have also noticed that some of their tubes emit a bluish-colored glow. There are TWO causes for this glow in audio power tubes; one of them is normal and harmless, the other occurs only in a bad audio tube.

* 1) Most Svetlana glass power tubes show FLUORESCENCE GLOW. This is a very deep blue color. It can appear wherever the electrons from the cathode can strike a solid object. It is caused by minor impurities, such as cobalt, in the object. The fast-moving electrons strike the impurity molecules, excite them, and produce photons of light of a characteristic color. This is usually observed on the interior of the plate, on the surface of the mica spacers, or on the inside of the glass envelope. THIS GLOW IS HARMLESS. It is normal and does not indicate a tube failure. Enjoy it. Many people feel it improves the appearance of the tube while in operation.
* 2) Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.

PLEASE NOTE: some older hi-fi and guitar amplifiers, and a very few modern amplifiers, use special tubes that DEPEND on ionized gas for their normal operation.

* -Some amps use mercury vapor rectifiers, such as types 83, 816, 866 or 872. These tubes glow a strong blue-purple color in normal use. They turn AC power into DC to run the other tubes.
-And occasionally, vintage and modern amplifiers use gas-discharge regulator tubes, such as types 0A2, 0B2, 0C2, 0A3, 0B3, 0C3 or 0D3.

These tubes rely on ionized gas to control a voltage tightly, and normally glow either blue-purple or pink when in normal operation. If you are unsure if these special tubes are used in your amplifier, consult with an experienced technican before replacing them.

ALSO NOTE: these light sources cannot be seen in metal-ceramic tubes, because their parts are opaque. As we said above, it is difficult to tell if a ceramic tube has become gassy. Usually, in a large radio transmitter, a gassy tube will arc over internally. (This does not damage the transmitter. It has protective circuits.) The equipment operating manual should give more information on this.
Stromberg Montreux
Schecter Hellraiser 7 String
Mesa Boogie "Son of Boogie" 100W Head
Mesa Boogie 112 Cab with a Celestion Vintage 30
Electro Harmonix Small Clone
Death By Audio Fuzz War

^^^ He has all the info you could want but just to inform you both of my amps have a blue glow to and nothing has ever gone wrong.
Peavey Vypyr 15
Peavey Windsor head
Avatar 2x12 with V30's

Custom Ibanez RG
ESP EC-1000
My bugeras glow blue just like that. if they werent blue i would be worried somethings wrong with the bias.

When you smoke a tube all that metal in the tube will look red hot like a toaster oven.. then you get that oh shzt noooooo feeling in your gut.
Gibson SG Standard
Gibson Les Paul Studio
Fender Partscaster
Bugera 6262
Jcm900 1960A