Tubes are glowing blue

[Always Broke]

Put a new quad of EL84s into my Peavey C30, and the tubes are glowing blue. A vast improvement from the horrid noise out of the amp, but it just doesnt look right. Should I be worried?

[Thundernotes]

Blue is fine - orange is bad. The blue comes from the ionization of small amounts of residual gas left in the tube. I read somewhere that it's the same thing that makes the sky blue, but I don't know how true that is.

[jaberwock]

I was told it was a sign that the vacum had had been compromised to some extent, and that minute amounts of the atmosphere were leaking into the tube; I'm not sure how true this is, but this was conventional wisdom back in the seventies when we used two, Hiwatt 200 watt amps as our PA; If any of the KT-88's started glowing blue, we took it as an indication they would need replacing in the next three months, and they were expensive even back then.

Jaberwock

[moozak]

I was told it was a sign that the vacum had had been compromised to some extent, and that minute amounts of the atmosphere were leaking into the tube

i think it's possible for a tube to have poor vacuum from the get go (mfg process) so i think there is some truth to that... but i doubt that all 4 have "compromised" vacuums... that's a bit different? i've also read some tubes (mfg process) can have minor impurities in them which can cause a "harmless" fluorescent glow.

either way... it might not hurt to have the bias checked though!

[jaberwock]

I was told it was a sign that the vacum had had been compromised to some extent, and that minute amounts of the atmosphere were leaking into the tube

i think it's possible for a tube to have poor vacuum from the get go (mfg process) so i think there is some truth to that... but i doubt that all 4 have "compromised" vacuums... that's a bit different? i've also read some tubes (mfg process) can have minor impurities in them which can cause a "harmless" fluorescent glow.

either way... it might not hurt to have the bias checked though!

It would normally be one pair of KT88'S that would start to glow increasingly blue as time went on; a new pair would glow a subdued orange. Those were fabulous amps, the wiring was the best I've ever seen, and they were incredibly LOUD.

None of my guitar amps have tubes that have glowed blue though.

jaberwock

[tbonesullivan]

There are several types of tube glow that occur.

Filament glow - when you put your amp on standby, the filaments warm up the tubes, and these have an orange glow. The filament is inside of the tube and usually is visible in some places.

Ionization glow: THis is a blue glow that surrounds the tube plate structures and occurs when the tube has voltage applied to the plates, so when you put your amp off standby and it starts making noise, you should have a bluish glow around the plates.

Loss of vacuum glow: This is a purple glow that indicates that particular tube has lost it's vacuum and is being contaminated by outside air. This is a signal to replace the tubes.

Red-plating: This is when the plates themselves start to glow orange. If this happens TURN THE AMP OFF IMMEDIATELY. This means the tube is overheating and will melt down if you leave it on. This is the equivalent of a "service engine soon" light in a car. Get that amp into a tech unless you are in the process of setting the bias current. Red plating means you have WAY too much bias current, and need to back it off majorly.