My amp caught on fire.

Jwoo

Member
Messages
183
Hello everyone. I need some help.

I just installed a set of THD Yellow Jacket (YJS) into my Hot Rod Deluxe. I bought them used off of a member on here. Everything was working fine before that.

After I installed them, I turned it on, and it made a loud buzz. Immediately after that, I saw something bright, I'm not sure what area it was in, i just panicked, turned it off, and unplugged it from the wall. I think it was near the phase inverter tube area. After that, it smelled like burning plastic, and I saw smoke.

I'm very afraid to turn on my amp again, and I'm afraid I damaged something. Why do you think this happened?
 

Jwoo

Member
Messages
183
Yeah, I'll do that for now. I talked to the guy before me, who also had it in the same amp, no problems.

I wonder if I did something wrong when I installed? I don't think I did...

I put the 6L6's back in. I'm afraid to turn it back on.
 

Jwoo

Member
Messages
183
Which fuse?

I looked at the back of the amp. I think my bias pot melted.

It should look like this:
BiasPot-5WResistors2.jpg


But mine has some red on it. I just turned it on with the 6L6s. It seems to be ok for now. I didn't play through it, but it didn't catch on fire again.
 

bilbal

Member
Messages
8,485
A very well-known, highly respected amp builder that post here (though veri infrequently), has said that those yellow-jackets are a problem waiting to expose itself. I guess you found that out personally!!! Hopefully others will read this and think twice before they use them. Thank God it's all that happened.

:nono :nono

Good luck,
b
 

Jwoo

Member
Messages
183
One of the plastic pieces that is in the center of the pins on the YJs broke off. Is this vital to the performance of the yellowjackets?
 

VacuumVoodoo

Member
Messages
1,546
One of the plastic pieces that is in the center of the pins on the YJs broke off. Is this vital to the performance of the yellowjackets?

Was it broken before you plugged in the YJ? It a guide pin that makes you plug the tube or YJ the correct way i.e. there are 8 pins that each must go into correct hole in the socket. If plugged wrong way many strange things can happen both to the amp and/or YJ. BTW that bias pot looks ok.

If you can post a close-up picture of the YJs bottom where the guide pin wasw broken off it may still be possible identify pin positions.
 

michael.e

Member
Messages
20,742
That lines up the proper pins in the socket. If you do not do that, you can fry something of course..

I had a pair of Yellowjackets for years and used them in all sorts of amps. Never had a problem. I don't buy the "problem waiting to expose itself" comment at all. All the units sold and problems seem to be next to none.

Emee
 

StompBoxBlues

Member
Messages
20,573
Which fuse?

I looked at the back of the amp. I think my bias pot melted.

It should look like this:
BiasPot-5WResistors2.jpg


But mine has some red on it. I just turned it on with the 6L6s. It seems to be ok for now. I didn't play through it, but it didn't catch on fire again.

Without a picture I can't tell for sure, but SOME manufacturers (not just amps but any electronics) use a touch of loctite or nail polish on trimpots after they set them to keep them from going out of trim. Also it is a good way to tell if they have been adjusted after.

I just looked closer at the picture (because you wrote "it should look like this" I thought this was a pic of a "normal" one...without the red but now I see the red you talk about) usually the thing I am talking about would be between the inner "screw slot" piece and the outer, but it might have the same function over on the side for all I know..
 

Jwoo

Member
Messages
183
Sorry for the confusion guys. That's actually not MY bias pot, but in fact, a pic of a normal one. Mine has a little more red than that, and StompBoxBlues' response explains that.

It seems to function normally with the 6L6's back in. I'll have pics of the YJs later.
 

Plague Dog

Member
Messages
2,608
It seems tubes by their nature are a problem waiting to happen. I've had el84's smoke on me more than once.
It's just the price of tone.

If the guide pin was broken off you probably plugged it in the wrong way, it may have damaged the YJ if it is working okay with the 6L6 back in place.
 

Jwoo

Member
Messages
183
The amp crackles intermittently now with the 6L6's back in place. This also happened after I did my speaker install, which I did right before the YJ's. Hmm...
 

Scott Auld

Administrator
Staff member
Messages
12,389
The amp crackles intermittently now with the 6L6's back in place. This also happened after I did my speaker install, which I did right before the YJ's. Hmm...


Is it possible that you wired the new speakers incorrectly, and provided the amp with too low impedance?

Take to tech ...
 

StompBoxBlues

Member
Messages
20,573
The amp crackles intermittently now with the 6L6's back in place. This also happened after I did my speaker install, which I did right before the YJ's. Hmm...

If you have a spare V1 tube (12AX7?) I would try replacing that to see if it helps the crackling (sometimes there ARE coincidences...and/or could be the damage did something there as well?) as that is often the culprit, but only after checking the speaker connections thoroughly.

If it still crackles, I also would take it to a tech and not try to use it more.
 

Jwoo

Member
Messages
183
I have some 12AT7s and a 12AU7 coming in this week. I will install those and see if that helps.

I also emailed THD about my problem, and they told me that when the locator pin is missing, it can cause the pins to not line up correctly, which would cause a bright flash/smoke. I am going to speak to an amp tech pretty soon.
 
Messages
6,116
The most comon problem with these amps,
and more than likely the problem here is an output tube socket arcing the PCB.
These two sockets are mounted on a PCB, and the space inbetween
the traces flashes over. I've repaired these manytimes over the years.
You have to remove the two output tube sockets to see this problem.
After I repair these I drill a small hole between the traces which stops
this problem from happening again.
 

Jwoo

Member
Messages
183
That was a very insightful reply, Roccaforte. Can you explain what a trace is, and what it means when it flashes over? I think that just might be it.

I reinstalled my YJ's (the CORRECT way, per THD's tech support), and it plays just fine. I still have that issue that I had before. According to the THD tech guy, when I installed the YJ's incorrectly, it just caused one of the EL84s to flash very brightly. But now it works fine, with the 6L6s or the YJs.

I am gonna take it to an amp tech this week, hopefully, and see if he can straighten things out.
 

StompBoxBlues

Member
Messages
20,573
That was a very insightful reply, Roccaforte. Can you explain what a trace is, and what it means when it flashes over? I think that just might be it.

I reinstalled my YJ's (the CORRECT way, per THD's tech support), and it plays just fine. I still have that issue that I had before. According to the THD tech guy, when I installed the YJ's incorrectly, it just caused one of the EL84s to flash very brightly. But now it works fine, with the 6L6s or the YJs.

I am gonna take it to an amp tech this week, hopefully, and see if he can straighten things out.

Traces are the connection lines on a printed circuit board. The lines really. They are used instead of wires to make connections. They try to make these as compact as possible, meaing a lot of the lines (traces) are very close together...the solder points, and test points (the silver part showing through in places) have a bit of solder on them...sometimes solder can just almost be touching another trace, and if the amp gets hot or something can actually touch...it's a mistake, usually because too much solder is used at that point. Soem pc boards though it is dangerous to drill because some use traces on both sides but also in the middle, and one could drill through a middle trace without intending to.

I think this is not something you want to do, but ask a tech if you have to take the amp in, to check for it and if the tech thinks it might be flashing over, the tech can fix it.
 




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