Bright Top JJ EL84

[Mark]

Hi,

I put a "new" set of 4 JJ EL84 valves in my KEL84 today just to hear the difference to the set of 4 Sovteks I have been using for a while and noticed one of the four was glowing a lot brighter on the top of the plates than the other three - see attached photo. I moved it to the other side and it did the same thing, i.e. the problem followed the valve. It sounds fine, but should I bin it in case it fails and takes other components with it ?

Thanks

Mark

[Phil Y]

Hi Mark,

Yes that does look very bright. I'm assuming that the brightness of the top mica is just reflected light accentuated by a long exposure?
I would take them out have a look at the offending valve with a magnifying glass if you have one. It could just be that the heater is sticking out of the cathode more than normal, in which case it may not do any harm. You should be able to see a central tube, this is the cathode, that emits the electrons and needs to be hot to do so. Can you see a white (possibly spiral)wire sticking out of the top of the tube? This is the heating element that glows orange when hot. Perhaps have a look and report back.

Phil.

[bob orbell]

Hi Mark, I have one new JJ EL84 tube, it is yours for the asking. Bob

[Mark]

Originally Posted by Phil Y

Hi Mark,

Yes that does look very bright. I'm assuming that the brightness of the top mica is just reflected light accentuated by a long exposure?
I would take them out have a look at the offending valve with a magnifying glass if you have one. It could just be that the heater is sticking out of the cathode more than normal, in which case it may not do any harm. You should be able to see a central tube, this is the cathode, that emits the electrons and needs to be hot to do so. Can you see a white (possibly spiral)wire sticking out of the top of the tube? This is the heating element that glows orange when hot. Perhaps have a look and report back.

Phil.

Phil,

Thanks. I have replaced all four valves with the original four JJ valves that all glow in the same places just to be on the safe side. I have a magnifying glass so I will play spot the difference this evening to see if anything is sticking out shedding light where I don't normally see it. The photo is pretty much WYSIWYG - there is no noticeable accentuation of brightness compared with a Mk 1 eyeball.

Mark

[Mark]

Originally Posted by bob orbell

Hi Mark, I have one new JJ EL84 tube, it is yours for the asking. Bob

Bob,

Thanks. That's very kind.

The top plate looked like it was glowing, but as Phil has pointed out it could simply be reflected light from a heater sticking out further than normal.

Let's see where I get to with a magnifying glass, before I take up your offer, which may be the safest way forward.

Mark

[bob orbell]

No problem Mark, if you need it just PM me your address and I will do the rest. The proper way to test this valve is to mesurer the heater curent of a good one and compair the readings with the bright one, I would suspect the heater element is partly shorted, it could even be making contact with the cathode. Bob

[TimN]

I would have thought a refund/replacement is in order if there is an issue with it?

[Mark]

Originally Posted by TimN

I would have thought a refund/replacement is in order if there is an issue with it?

Tim,

In normal circumstances yes. However, the "bright one" is part of a free extra set of JJ EL 84 I got from WAD over 10 years ago when I bought the amp kit. This may have been around the time I was concerned about out-of-spec ECF80 voltages when they gave me a few spare EI/Edicron ECF80s to try as well. So I didn't pay for them, I have had them for more than 10 years, and WAD is long gone, so it wouldn't be possible for me to be so rude to ask for a replacement :-).

Mark

[Mark]

Originally Posted by Phil Y

Hi Mark,

Yes that does look very bright. I'm assuming that the brightness of the top mica is just reflected light accentuated by a long exposure?
I would take them out have a look at the offending valve with a magnifying glass if you have one. It could just be that the heater is sticking out of the cathode more than normal, in which case it may not do any harm. You should be able to see a central tube, this is the cathode, that emits the electrons and needs to be hot to do so. Can you see a white (possibly spiral)wire sticking out of the top of the tube? This is the heating element that glows orange when hot. Perhaps have a look and report back.

Phil.

Phil,

I played spot the difference between my "bright" JJ EL84 and a normal one last night with a x10 magnifying glass. The only difference I saw was one of the pins in the bright EL 84 was significantly longer than the one in the normal EL84 - see diagram attached. I can't see that being the cause of the extra brightness. The heights of the heater tubes in the middle were effectively identical and the heater did not stick out of the tube. I am no expert, but I suspect finding someone with a valve tester and seeing how much current the heater is drawing as Bob has suggested might be the way to go.

Mark

[Phil Y]

Hello Mark,

I couldn't get your pdf to open, my tablet said it is corrupted. No matter, you have other valves and anyway, EL84s are not expensive, probably safest to get rid of that one. Unless as you say, someone can check it for you on a tester.

Phil.