EL34 rocking in the house of blue light.

[Diabolical Artificer]

Powered my big amps yesterday and noticed a blue light in one, I know some valves do this and am not overly concerned, it went away after a minute or so. i was really smitten by how deep the electric blue was, actually caught on camera, see pic. The only thing "wrong" with the valve is that the top mica looks a bit askew.

Andy.

[Aub]

Great pic Andy. I guess all you can do for now is to see if it happens again after the amp's been off.

Cheers

Aub

[Radio Wrangler]

A bit gassy until the getter gets going as it warms up. As it cools, adsorbed material can evaporate again. Probably the outgassing process wasn't left long enough in manufacture.

David

[Hartley118]

Likely to be fluorescence of the glass envelope. Even better than the EL34, 807s can be great performers of such a light show - more spectacular when accompanied by a subtly red hot anode. All pretty normal in a hardworking power valve.

Martin

[Heatercathodeshort]

The clue here is that the blue glow is focused on the glass. Many power output valves do this. EL34s 807, PL38 etc. If the blue glow is an internal 'fog' the valve is almost certainly gassy and useless. I would stick my neck out and say, nothing to worry about. J.

[Radio Wrangler]

Needs a couple of views at different angles to show whether the light source is inside the anode or a patch on the class.

It does look a bit insufficiently defocused for gas, so maybe it is glass fluorescence.

David

[GrimJosef]

It can depend very much on the impurities in the batch of glass. I recently bought some old-stock Russian 6C4Cs (equivalent to the US 6B4G). They looked identical inside and all had the same factory markings. But three had one date code and the fourth a different one (maybe a year or two's difference). The odd one glowed bright blue, the other three not at all.

Cheers,

GJ

[Glowing Bits!]

This phenomenon tends to happen on a Pioneer ER-420 every time I power it up, it stops when the cathode starts glowing, it has never caused a problem.
Is the OP's amp fitted with a solid-state rectifier by any chance?
If so, that's why it's doing what it does, it would be best to delay the HT until the cathode starts to warm up.

[Glowing Bits!]

Originally Posted by Heatercathodeshort

If the blue glow is an internal 'fog' the valve is almost certainly gassy and useless.

An internal fog is an understatement, I've seen valves lighting up the place in a turquoise colour before now, followed by cabinet rattle from the speaker humming loudly, plug withdrawn in quick succession after that!

[mark_in_manc]

Thanks for posting that pic Andy. I've some Russian 6L6-a-likes which do this, and I worry about it now and again

[Diabolical Artificer]

Thanks all, so it's glass florescence? It is outside the anode and looks to be right on the glass.

Yep SS rectified and delayed HT Rick though i think a few more seconds would be beneficial.

I wish that the all the valves would glow this pleasing blue,all over, it is really rather fetching and mesmerising.

Andy.

[Heatercathodeshort]

An internal fog is an understatement, I've seen valves lighting up the place in a turquoise colour before now, followed by cabinet rattle from the speaker humming loudly, plug withdrawn in quick succession after that!

A very common fault with the early PY32 H.T. rectifiers used in television receivers, particularly the Ferguson 306T was 'gas'. The rectifier glowed so brightly that it projected a pink silhouette of the cardboard back onto the wall behind! After a period of time this would slowly recede and the picture would slowly build up. When the delay approached an hour It was time to call the telly guy.

The EL84 often exhibited a sharply focused internal low level blue pattern around the anode area, again not an actual fault. John.

[bikerhifinut]

Originally Posted by Heatercathodeshort

A very common fault with the early PY32 H.T. rectifiers used in television receivers, particularly the Ferguson 306T was 'gas'. The rectifier glowed so brightly that it projected a pink silhouette of the cardboard back onto the wall behind! After a period of time this would slowly recede and the picture would slowly build up. When the delay approached an hour It was time to call the telly guy.

The EL84 often exhibited a sharply focused internal low level blue pattern around the anode area, again not an actual fault. John.

Johns correct about the EL84, both they and its big brother the EL34can display an internal blue glow inside the anode, this is perfectly normal behaviour.
Likewise its a known effect on certain KT88 bottles, (and no doubt other types) especially the soviet ones where the glass envelope can display a fetching blow glow. Usually only visible in very low light. Caused I read, by the composition of the glass used whether its impurities or its molecular structure I couldn't say, but it does look nice!
I'd just keep an eye on it Andy but the "Blue glow of death" is a fairly easy thing to spot, when any of my valves have done it the blue haze has to my perception had a slight pinkish tinge to it. Got to be careful here as colour vision varies in individuals.

A.

[Techman]

Originally Posted by bikerhifinut

I'd just keep an eye on it Andy but the "Blue glow of death" is a fairly easy thing to spot, when any of my valves have done it the blue haze has to my perception had a slight pinkish tinge to it. Got to be careful here as colour vision varies in individuals.

Yes, I agree. They often flash over internally when like this and blow the fuse...if there's one to blow!

[Radio Wrangler]

Blue with pinkish tinge is characteristic of low pressure discharges in air.

David

[Glowing Bits!]

So far, others agree there's nothing wrong with it.
Apparently, slightly soft valves sound better, whether that's true is open to debate.
The one to watch out for is bright turquoise, it kills the output tranny, rectifier and whatever else is nearby!
Given how the deep blue glow disappears after warm-up would suggest the valve is in good condition, otherwise it would stay there forever, getting progressively worse over time.