EL84 fireworks

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mentalmuso
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EL84 fireworks

Post by mentalmuso »

Hi there, new to this forum but have been perusing this site forever. I'll cut to the chase, I have an 18watt that I built about 10 years ago, not used much but was a very successful build. Great tone etc etc. Well I took it out of storage the other day and found it had a broken el84. I swapped the pair out for some old Sylvania 6bq5/el84 I had lying around, powered the amp up, and after about 5 sec one of the el84 sparks profusely internally.

Can someone guide me through diagnosing and testing the voltages etc to make sure it's not the amp circuit but in fact just dodgy tubes? I've ordered new el84s but want to be sure the amp isn't going to kill them.

Edit.. I have tested the voltages after the main caps and all seem to line up with diagrams I have. I just want to be sure I haven't missed anything.
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JMPGuitars
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Re: EL84 fireworks

Post by JMPGuitars »

Sounds like bad tube, especially if the voltages look good. The easiest way to confirm is to swap the tubes around, and you'll see the sparks follow the tube. That's assuming the tube has any life left. Sometimes a tube sparks and that's the end of the story.
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Re: EL84 fireworks

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Thanks, I had 5 different tubes I tried but they were all same age and type out of an old Hammond organ. Maybe they were all toast. I'll try my new tubes when they arrive. (I bought 2 pairs just in case haha)
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Re: EL84 fireworks

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mentalmuso wrote:
Sun 05/22/22 10:20 am
Thanks, I had 5 different tubes I tried but they were all same age and type out of an old Hammond organ. Maybe they were all toast. I'll try my new tubes when they arrive. (I bought 2 pairs just in case haha)
If they all sparked, that's suspicious. Try the tube swapping idea, see if the sparks are only in one socket, or if they follow the tubes in question.
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Re: EL84 fireworks

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JMPGuitars wrote:
Sun 05/22/22 10:37 am
mentalmuso wrote:
Sun 05/22/22 10:20 am
Thanks, I had 5 different tubes I tried but they were all same age and type out of an old Hammond organ. Maybe they were all toast. I'll try my new tubes when they arrive. (I bought 2 pairs just in case haha)
If they all sparked, that's suspicious. Try the tube swapping idea, see if the sparks are only in one socket, or if they follow the tubes in question.
Initially, they were all in one socket, but the very last one I tried was in the other socket. So yeah I dunno. I think it's best to just be ready to sacrifice new tubes if it comes to that.

Can I run the amp on only one power tube in a push pull scenario? Just to test? I know I have one good JJ tube.
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Re: EL84 fireworks

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mentalmuso wrote:
Sun 05/22/22 12:23 pm
Initially, they were all in one socket, but the very last one I tried was in the other socket. So yeah I dunno. I think it's best to just be ready to sacrifice new tubes if it comes to that.

Can I run the amp on only one power tube in a push pull scenario? Just to test? I know I have one good JJ tube.
No, put both tubes in. JJ tubes are trash when it comes to reliability, but if it's an older JJ, it might be okay. All you need to do is fire up the amp and see if only 1 tube sparks. If it's only 1 tube, then swap the two power tubes around and see what happens.
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Re: EL84 fireworks

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JMPGuitars wrote:
Sun 05/22/22 2:06 pm
mentalmuso wrote:
Sun 05/22/22 12:23 pm
Initially, they were all in one socket, but the very last one I tried was in the other socket. So yeah I dunno. I think it's best to just be ready to sacrifice new tubes if it comes to that.

Can I run the amp on only one power tube in a push pull scenario? Just to test? I know I have one good JJ tube.
No, put both tubes in. JJ tubes are trash when it comes to reliability, but if it's an older JJ, it might be okay. All you need to do is fire up the amp and see if only 1 tube sparks. If it's only 1 tube, then swap the two power tubes around and see what happens.
What do you recommend for midrange el84? Brand I mean
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Re: EL84 fireworks

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When you say sparks, do you mean it just flashes at power-up? Or are there prolonged sparks until power is off? Hammond used a lot of mullard tubes (among others) and the brief flash at startup is normal for mullards, although not all exhibit this flashing....

I have several on my JTM50 build that flash at startup and sound ***great***

They test as new on my Sencore TC162 solid state tube tester.
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Re: EL84 fireworks

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I use old Russian 6p14p or NOS Sovteks. They're priced very decent and are very sturdy. They sound great too IMHO.
https://youtu.be/DJde9deFb0M
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Re: EL84 fireworks

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mentalmuso wrote:
Sun 05/22/22 7:06 pm
What do you recommend for midrange el84? Brand I mean
I like new production Mullard or TungSol, but they're not really available right now.
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Re: EL84 fireworks

Post by JMPGuitars »

Bieworm wrote:
Sun 05/22/22 10:37 pm
I use old Russian 6p14p or NOS Sovteks. They're priced very decent and are very sturdy. They sound great too IMHO.
https://youtu.be/DJde9deFb0M
Even those have gone up in price significantly with the war.
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Re: EL84 fireworks

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JMPGuitars wrote:
Mon 05/23/22 6:15 am
Bieworm wrote:
Sun 05/22/22 10:37 pm
I use old Russian 6p14p or NOS Sovteks. They're priced very decent and are very sturdy. They sound great too IMHO.
https://youtu.be/DJde9deFb0M
Even those have gone up in price significantly with the war.
It's a sad thing. I bought a batch from a supplier in Ukrain though. 3 weeks after the order they arrived. I paid like 3 or 4 € a piece for NOS Reflector 6p14p tubes 👍👍👍

And my new builds all sport Voskhod 6N2P preamp tubes. They are excellent!!! Non interchangeable with 12AX7 though.. but I don't care.

BTW, that new reverb unit I built is awesome!!! no hum this time..
Poseidon Reverb schematic-DG00022-2.pdf
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Re: EL84 fireworks

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Bieworm wrote:
Mon 05/23/22 6:54 am
It's a sad thing. I bought a batch from a supplier in Ukrain though. 3 weeks after the order they arrived. I paid like 3 or 4 € a piece for NOS Reflector 6p14p tubes 👍👍👍
I ordered some "used, working" 6p14p tubes for just a little less than that 3 weeks ago, still waiting though.
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Re: EL84 fireworks

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JMPGuitars wrote:
Mon 05/23/22 7:05 am
Bieworm wrote:
Mon 05/23/22 6:54 am
It's a sad thing. I bought a batch from a supplier in Ukrain though. 3 weeks after the order they arrived. I paid like 3 or 4 € a piece for NOS Reflector 6p14p tubes 👍👍👍
I ordered some "used, working" 6p14p tubes for just a little less than that 3 weeks ago, still waiting though.
lol.. on the gambling tour too I guess.. Out of the 12 I bought from Ukrain one was bad.. that's a good thing I think. The war forces us to get creative, but drags us out of our lazy chair and do something different from what we're used to. Maybe we end up having better alternatives, who knows?
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Re: EL84 fireworks

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Bieworm wrote:
Mon 05/23/22 7:10 am
lol.. on the gambling tour too I guess.. Out of the 12 I bought from Ukrain one was bad.. that's a good thing I think. The war forces us to get creative, but drags us out of our lazy chair and do something different from what we're used to. Maybe we end up having better alternatives, who knows?
I bought them to run through my tester, not for my amps. I figure if I get at least one decent pair out of the 8 I ordered, that's a bonus.
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Re: EL84 fireworks

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Unit_1 wrote:
Sun 05/22/22 10:33 pm
When you say sparks, do you mean it just flashes at power-up? Or are there prolonged sparks until power is off? Hammond used a lot of mullard tubes (among others) and the brief flash at startup is normal for mullards, although not all exhibit this flashing....

I have several on my JTM50 build that flash at startup and sound ***great***

They test as new on my Sencore TC162 solid state tube tester.
It was a lot of snap and popping in the speaker accompanied by blue flashing with trailing sparks inside. It was great.
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Re: EL84 fireworks

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Just to let you all know, new JJ tubes went in and seem to be working fine. Thanks for all the help
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Re: EL84 fireworks

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mentalmuso wrote:
Thu 05/26/22 8:09 am
It was a lot of snap and popping in the speaker accompanied by blue flashing with trailing sparks inside. It was great.
Oh, that is fun! I had somebody bring me an amp with a similar tube. Instead of blue, it was purple, and it did eventually spark and die. I recorded it before it died: https://www.instagram.com/p/CdJVToTAdyZ/
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