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spacemen12 10th January 2011 04:11 PM

EL34 not glowing anymore on SimpleSE
Last year a built a tubelab simpleSE with edcor transformers. The amp worked from day one, until now.

Now it is working only on the left hand side. The EL34 filament on the right hand side is not glowing anymore. What can I do to test that? I don't want to swap tube, because if it is a problem that blows tube, I will burn the other one. And if it is a faulty tube, I don't want to damage the other circuit.

Is there a simple test/measurement that you can suggest?

Best regards,

rknize 10th January 2011 04:16 PM

If the filament isn't lit, it is most likely a bad solder joint on your socket or possibly on the pin of the tube. Unless something is horribly wrong with wiring, you won't ever burn out a tube filament. I would swap the tubes and then you will know...but you may find after doing that that both tube work again. :)

Ty_Bower 10th January 2011 04:22 PM

You could pull the tube and check across pins 2 and 7 to verify the heater isn't open circuit. You should have no more than a couple ohms resistance across the cold heater.

You could also stick your voltmeter probes into pins 2 and 7 of the EL34 socket while the amp is powered on. You're looking for roughly 6.3VAC here. I'd pull the rectifier tube to minimize the exposure to high voltage. If your amp uses solid state rectification, make sure the rectifier switch is open and be extra careful.

spacemen12 10th January 2011 04:45 PM

Thanks for fast responses.

Resistance from pin 2-7 < 1 ohm
Voltage from 2-7 6.3VAC without the vacuum rectifier (no SS rectifier present).
It is in fact not a tube issue (swap cause no problem).

After measurement, replace the tubes and the music is there again on both side... but for how long? I will look at the solder later, cannot open the amp right now.

Thanks a lot.

Ty_Bower 10th January 2011 04:50 PM

It could be a cold solder joint where the tube socket meets the circuit board. It is just as likely a dirty socket pin. Taking the tube out and putting it back in cleaned it good enough and now it goes again.

rknize 10th January 2011 06:21 PM

Had a feeling. My moneys on the solder joint. The solder pads for the sockets have to deal with both thermal and physical stress of tube insertion/removal. George warns about not using too much solder on these pads so that solder doesn't flow into the pin hole. It's good advice because the entire socket pin is tinned and solder will happily flow there.

However the holes are large and the metal of the tube pins is thin, so if there isn't enough solder the joint will fracture over time. You can be a bit more generous by reflowing the pin with the board right-side up and adding solder from the top instead of the bottom. Then you have gravity on your side.

spacemen12 10th January 2011 09:02 PM

Well well well...

The sweet music was back, but I decide to swap the tube, from left to right. Play stereo for a 30 minutes, then the left is gone (no sound and no glow).

It takes about 30 minutes of heating and then fade out. So it works, if I let it cool down.

My guess is a bad tube (Electro-harmonix EL34 rated at IP=39, GM5800 bought from partsconnextion last year). Is a a normal lifetime for this tube? What next should I buy (single tube, or a pair because the other one is about to die as well)?

Is there potential problem of listening to mono with both el34 in? Cannot really live without music...

My use is about 10 hours a week in a pet free, children free environment. I play at low volume, because I am in an apartment complex.

Peckerwood 10th January 2011 10:17 PM

I think that assuming it is a class AB amp then the one that is still glowing is bad and the one that is not is good. That might not always be the case but I have seen it several different times.

You could probably get away with buying a single tube but the best thing would be to buy a matched pair. They will last longer probably.

10 hours a week they should last longer than a year if they are matched and not biased too hot.

rknize 10th January 2011 10:20 PM

So the issue followed the tube? You can try reflowing the solder on the two tube pins for the heater (2 and 7). Otherwise,'s a defective tube not a tube wear issue.

It's an SE amp. You can run with just one tube. To be safe, I would just remove the bad tube completely in case it does have some internal problem that could result in a short that could cause other damage to the amp.

rmyauck 11th January 2011 12:35 AM

Take a close look at the filaments of both tubes where they connect to the pins and compare them.

You should see if one is broken.

I don't think they would reconnect themselves and then disconnect after 30 minutes. Tube filaments are like on a light bulb so when they break that's it, unless it's dangling around where it should be connected. You should see that. DHT tubes of course are different.

It's got to be a bad connection in either the socket to pin maybe not tight or solder to tube socket. It's possible to have a bad connection i in tube base, but highly unlikely. I read some of the pins on some of these new tube sockets loosen up because of heat. Quality of metal can be poor or wrong type to deal with heat. Try using a pick like a dental tool to bend pins so they fit tight. Check and tighten all your socket pins.

You should get get a double that life at least I would think. They say at least 2000 to 3000 hrs on PP amps, but they can be easier on tubes.

One thing that is hard on filaments is the startup on the cold filaments. The more starts the lower the life too for tubes. That's where light bulbs fail.

Do you have ICL's on PS? I wonder if just using a low cost light dimmer hooked up on your line cord would solve the problem better. I read tubes like to come up slowly over a minute or so and the same going down for the best life. I don't think there would be any noise as long as the dimmer is turned up to the full position. Maybe one would still have to have a switch to bring in a full connection without the dimmer pot once up to full voltage.

You have the 5AR4 , which should help with a slow filament startup right?

Hope that helps!

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