Brand new tubes.....strong metallic burning smell?

Is this normal?

I installed new JJ tubes no smell, but they didn’t work out in the end. I next installed new Tungsol EL34b matched quintet. And now there is a very strong metallic burning smell that raises from the amp once warmed up. I’m collectively 4 hours into these tubes?

 

Are these for your Jolida JD1000RC? Does that amp have a bias control? If so, has the bias been set correctly? Are the tubes red plating?

 

Nope. I’ve used the self biasing built in 3 times over the last 4 hours of use. Each time it’s been very very close and any adjustments have been extremely slight.

Two different tube repair shops have manually adjusted bias using other tube combinations, and have found the self biasing to be very close while just a tad on the warm side. I set the auto biasing as cool as possible by coming to the red light coming on and keeping just the slightest touch back keeping it from red. Basically they randomly come to red on their own but not steady.

No red plate anywhere. The tubes look totally normal.

 

Another two hours, same smell.

 

Different tubes = different bias. They are probably dissipating too much heat from overcurrent and causing the glass, bases, and sockets to get too hot. An infrared thermometer is a useful tool in diagnosing, you can get the exact temperature of tube bases or even internal components.

You won't truly know what's up unless you use a multimeter and insertion-style tube base test probe to test the current draw of each tube. Test points or calibration built in to equipment requires that the current measurement resistors not be out of spec or damaged, and also may not indicate total current from leaky coupling or bypass capacitors.

 

Pretty normal I think. I have used tubes since the mid eighties and every now and then you get a set that smell when hot. One set I had (Svetlana) took a week for the smell to go. Think it is do do with the cements used and base material. If all else checks out, bias etc and assuming that the tube spec matches the amps design then you may have to put up with a smell for a few days. Open some windows, don't go out and leave them on, be cautious but the smell should recede

 

If the tubes are not red plating - I'd look at the boards - just to make sure - everything looks fine (clean caps/etc no buldges/burns) - and board doesn't stink - and if that is the case - just keep an eye on it there could have been some coating on the glass that is burning. You could try cleaning the glass with alcohol (with the amp unplugged) - I don't as I don't want to lose the lettering on my more $$ glass.

I don't understand your bias comments - I use a volt meter - and as long as the bias is correct and stays pretty constant w/o creeping - then all is well.

Good luck!

 

I once had a pair of Russian EL34’s labeled ‘Groove Tubes’ and they stunk when I first installed them. They were (I believe) biased correctly, yet the orange lettering on them would cook and smell bad. Eventually the orange paint turned brown, and then the smell finally stopped. Perhaps this is a similiar problem.

 

Thanks everyone for the replies. The amp a Jolida JD1000rc has a feature to help in biasing it. There are little red lights near each tube. As you very slowly turn the biasing adjusting screw the light comes on. When it comes on it should be set within spec. I took my amp to two other shops for another reason and both places set the bias using a multimeter and yes one even had and did use a thermal infrared tool to check things. With multiple sets of tubes they (both shops) shared with me that the little self help biasing red light was pretty darn close and defiantly usable. So I have confedence that these tubes are very close to correct. I also am saying that when that red lighting comes on I sort of just touch the screw and “think” about turning it back, jsut enough to have the red light faint. YOu cant even really feel the screw move. But if you touch it it goes red.. its that close. I do this so its on the normal or perhaps cool side.

 

Ok, so now V5 is red plating. First I’ve seen that. What does it mean? Cool and re-bias... again, or other issues?

 

It seems like you're doing everything your amp allows you to do in terms of bias, and still having problems. If these were Mullard XF1's from 1952 I'd blame the amp (right or wrong), but since they're relatively inexpensive contemporary tubes, I'd blame the tubes.

 

Yeah it’s fine with the one tube replaced with an old one. I guess Igo for round three withthe tube seller.... this tung sol EL34b is toast.