Valves colour?

suspiciousminds

Since my laney played up, i've been reading up on valve amps but from what i've read, they're supposed to glow blue?
Mine glow an orangey red at the top and bottom of the el34's.
Is this correct - or is my mind playing games because i happen to be colourblind?

digitalscream

You can get valves which glow blue, but they're pretty rare. Orange is much more common. A bright red is generally scaryscary time.

ICBM

Good glow:

Orange at the top and bottom in the centre - this is the valve filament.

Blue (sometimes slightly purple-ish) on the inside of the glass - fluorescence caused by minerals in the glass - indicates a good vacuum and is most common in high-quality US-made valves. You might not see it easily except in a dark room.

Blue (sometimes slightly green-ish) inside the plate structure (visible through the slots or holes, often only if you look at just the right angle) - ionisation of trace gasses in the valve, but not a problem unless it's really extreme.

All these indicate the valve is operating normally and correctly - contrary to the popular myth that blue glow is bad!

Bad glow:

Red in the plate structure itself - either the whole thing, a patch in the middle or just faintly along the seams - this is "redplating" and means the valve is running too hot, usually because the bias is too low. If it's dull or faint you may not see it easily except in a dark room and isn't too serious, although not good and still needs fixing. If it's strong and bright it indicates imminent failure - turn off immediately.

Orange glow inside the plate structure when the amp is being played hard - screen grid overheating. You can usually seen the grid wires themselves glowing orange or bright yellow if you look carefully at the right angle through the slots. Not always instant bad news - some amps tend to do this a fair bit - but not good for valve life and at worst it can cause failure.

Pink or pinkish-purple glow of any kind - always bad, it indicates major gas leakage into the valve and very imminent failure. Sometimes accompanied by visible arcing or bright plate glow, in which case turn off as fast as you can!

Cirrus

There's two little coils of wire that go right up the middle of the valve and glow orangey yellowish. That's the heater element. Then there's a weird ethereal blue/purple glow that hangs in the vacuum inside - you can typically only see it if the room is quite dark and you look at the valve from the right angle to see through the holes in the plates.

If the plates (the metal sheets on the outside) are glowing at all, they're too hot and the valve needs to be biased cooler. They start a dull cherry red when they overheat and the hotter they get the brighter they glow.

If bolts of lightning are coming from your valves or flames erupt from them, those are also bad signs. Finally, if the silver coating on the inside of the glass at the top turns white it's game over: you let the vacuum out.

suspiciousminds

Thanks guys, sounds like mine are ok then.

57Deluxe

I like it when they glow blue.... and the slight ssshhh-ing sound they make - is as if they are giggling playful children...

gubble

If you purchased a Marshall MA series amp you can be sure the valves will only glow bright red !