Help, Smoked My Transformer

[fisheric]

Hi guys. I have an old guyatone 70's tube amp with 3 12ax7s 1 12at and 2 6l6s. I think its a mesa boogie clone or a fender variant, im not sure.

When i got the amp it didnt work. I took the chassis out and one of the resistors was fried. I replaced that and the amp was working really well and sounded good at low volume. Today i was playing it with the chassis still out of the amp and i noticed a little bit of smoke coming from one of the 6l6 tube sockets. i immediately turned the amp off to stand by and as soon as i hit the switch a good sized puff of smoke came out from under the board where the transformer is.

I am almost postitive that it was transformer smoke and not a component on the board.

I am afraid to turn the amp back on, is there a way to test to see if the tranny is still good? i would hate to lose it because it is a HUGE tranny. Bigger than most 100w amps i have seen.

[Delta2Brewtal]

Just check the primary and secondary windings for resistance/continuity?

[SatelliteAmps]

Trannies don't smoke so much as just short. Cap's usually smoke, big puffs of smoke.

[Jade]

Fisheric,

It sounds like something simple like a bad power tube, or the bias being way off. If you like the amp, I suggest you take it to a tech, and have it looked at. Power supply issues are some of the quickest, and easiest problems for a tech to find, and fix. Assuming that the transformers are indeed OK, which they should be, You' have it fixed for a relatively small amount, and have an amp you can enjoy for a long time. If you keep experimenting with it yourself, and just replacing parts that burn up, you're not really finding the problem, you're just inflicting more damage to the the amp. I mean, there's a reason parts smoke, and that smoking part is not usually the cause of the problem, but simply a symptom of something else you cant see.

Be safe, and take it to someone:)

Jade

[RussB]

I am almost postitive that it was transformer smoke and not a component on the board.



That's faulty thinking. The bottom line is you have no idea what could be wrong, you're just speculating

[donnyjaguar]

Here's my speculation. Bad output tube or bias circuit causing it to go into thermal runaway.

[Structo]

If you have ever smelled a fried transformer, you would know it.
Very unique type smell.

[SatelliteAmps]

Again, if you saw smoke, chances are it is a cap that popped. If you want to find out, open the amp, and look at the caps to see if one is exploded. If your tranny smoked, there should be physical signs of that as well.

[fisheric]

yes, it was really stupid of me to mess with that amp. and no the tubes weren't biased properly.

If the smoke had come from one of the capacitors wouldn't the cap has tell tale signs like discoloration or burn marks?

I called up Tube Sonic amp repair here in Sacramento. I've dealt with the guy before in the past and he is pretty cool.

Damn, I shoulda just taken it into the shop in the first place.

Ill let you guys know how it turns out. I should get the amp back in a week or two. Thanks for you guys help and hopefully my amp will pull through.

[fisheric]

OK, I took it over to the amp repair shop and Shane, the owner, took out all the tubes and put it on a variac and proceeded to check voltages in different places. When he was satisfied that the tranny was still good (woot!) he put in and biased the tubes.

The resistor I replaced was the wrong value by a long shot, but after biasing the tubes we played it through a 4x12 and it sounded great.

He is gonna replace the bad resistor, the electrolytics and just a couple other capacitors. most of the caps on the board are all PIO and he said those are really good.

Oh and best part is im gonna get a whole set of NOS tubes from him. He also has alot of "pulls" from projects that he has accumulated over the years that he sells really cheap so I am gonna stock up on some 6l6s and el84s.

Thanks for everyones help. If anyone reads this thread there is a lesson here to be learned. Don't F with stuff you know nothing about.

[Jade]

Hey man,

Glad to hear it's got a clean bill of health, and getting a good cap job! You should be good to go for a long time.

Cheers!
Jade

[fisheric]

Well everything has been fine.

Except I went through two sets of cheap 6l6s. Got a set of tung sol 5881 and everything has been okay.

Tonight I blew a fuse so I went and got more and as soon as I turn the amp on it blows a fuse.

and I am suppose to audition tomorrow for a band...

[fisheric]

oops. did something stupid. when i bought the new pack of fuses i set it down next to a pack of 1amps for something else.

when i put in the 3 amp everything was okay, but i am still afraid to turn it up as loud as i had it the first time.

[RussB]

I don't know where to start...

Did you burn up 2 quads of the pulls you got from Shane?

What is the proper fuse rating for your amp?

[fisheric]

I don't know where to start...

Did you burn up 2 quads of the pulls you got from Shane?

What is the proper fuse rating for your amp?


they were two pairs. One was a new pair that I got from Jim at little dog amps. They were TADs. Those are the ones that were in the amp, when I first had trouble with it. When I got it fixed Shane gave me a set of used mesa boogies which went bad. He replaced them with USA made tung sols which are still fine.

I told Shane that it seemed strange to me to have two sets of power tubes in a row fail. He checked the amp out and checked the tubes out and told me that even though it seems strange it was just a coincidence.

I guess im just jumpy now. When the TADs and boogies failed there was smoke and me freaking out thinking the amp was toast.

I did talk to him about adding a fuse that would blow in the event of a power tube failing.

The proper rating is 3 amp. I bought both packs at the same time.