Amp smoking. Help!

[Pete Farrington]

Pete, your name is familiar and you seem quite knowledgeable. Are you an amplifier designer and builder?

Only on a DIY basis, perhaps you might have clocked my avatar on other amp techy forums. I usually go by ‘pdf64’ but that didn’t seem to work out when I signed up here.

 

[jgab]

That was really cool!

Take it outside and play it again until it bursts into flames. Who doesn't want to see this?

Who cares what it's worth. Ha Ha

 

[mcblink]

Nasty habit. You should have a talk with it.

Been through it with one of mine before....

It's a bad deal...

 

[351]

A winding is just a piece of wire wrapped around the iron centre of the transformer.
There's a few wires or windings in the power transformer.
Primary winding and secondary windings.
As the winding shorts out in the power transformer, it has less resistance because the length of the wire is shorter as it's shorting on itself.
Because it has less resistance, the current from the wall socket, the mains, is flowing through the shorted Primary winding too fast, the winding cannot handle it and gets hot.
Either that or the secondary winding is shorted and the energy that is being reflected to it from the undamaged Primary winding is overwhelming the now shorter secondary winding. same thing, the shorter length of wire has less resistance and as such is getting hotter than normal.
You can find out if it's the Primary or the secondary that's shorted pretty easy with a multimeter.
The shorted winding which is hot is burning the plastic or paper sheaths that cover the windings creating smoke.
I recommend triode electronics for a good cheapish power transformer.

 

[Pete Farrington]

It’s not so much the drop in resistance so much as the shorted turns sucking all the energy out of the magnetic field, causing the winding inductances to collapse. So winding impedance becomes pretty much the same as winding resistance.
So the primary draws far more current, firstly because the shorted turns are drawing fault current via the relevant turns ratio, secondly because the magnetic field has disappeared and the primary is now just effectively a coil of wire across the mains.

 

[myersbw]

Ok, I'm going to point out something that...maybe was addressed? I didn't see it specifically addressed?...anyways, I'm seeing three separate photos that clearly show the power cord. And, only three wires from it....brown, blue, green (chassis ground). In the first photo (earliest post), the blue is tied to orange and off to the side of the cap. However, in the following post, I see the blue/orange wires tied to the positive terminal of the cap?? (Let's just ignore the hanging white wire for now.) (Specifically, look at the power cord wiring in post 47)

So, at one point, the 240vac feed was literally tied to the B+ cap? It's no surprise everything was going up in smoke. I'd be replacing all those caps and a whole lot of testing needs to happen. Like Pete referenced regarding the caps venting...at least now it's no surprise why.

If you were just smoking caps, you may have got lucky with the PT...the alternating voltage likely cooked the caps without exceeding the current draw for blowing the fuse. Either case, please don't just 'replace parts'...get it to a tech with the proper equipment to ensure nothing else is compromised you can't see (or smell??? lol)

Good luck!
Brad

 

[351]

Ok, I'm going to point out something that...maybe was addressed? I didn't see it specifically addressed?...anyways, I'm seeing three separate photos that clearly show the power cord. And, only three wires from it....brown, blue, green (chassis ground). In the first photo (earliest post), the blue is tied to orange and off to the side of the cap. However, in the following post, I see the blue/orange wires tied to the positive terminal of the cap?? (Let's just ignore the hanging white wire for now.)

So, at one point, the 240vac feed was literally tied to the B+ cap? It's no surprise everything was going up in smoke. I'd be replacing all those caps and a whole lot of testing needs to happen. Like Pete referenced regarding the caps venting...at least now it's no surprise why.

If you were just smoking caps, you may have got lucky with the PT...the alternating voltage likely cooked the caps without exceeding the current draw for blowing the fuse. Either case, please don't just 'replace parts'...get it to a tech with the proper equipment to ensure nothing else is compromised you can't see (or smell??? lol)

Good luck!
Brad

this is a good call

I am now wondering
' why is the power cord hooked up like that'
and now I'm thinking
' is it because the person thought b+ is neither dc nor ac, it's just ' electricty B+?'
I guess the caps may not mind as much as I first thought?
They do after all process rippling DC if not fully blown AC from the wall.
now I'm thinking
' should I repeat this in an experiment for no particular reason, just to see what happens?' ( not in an amp, on the bench with a cap and a power cord).
now I'm thinking
' i'd better put the dog in a room upstairs beforehand, open the windows and have a room fan handy.'

 

[351]

Ok, I'm going to point out something that...maybe was addressed? I didn't see it specifically addressed?...anyways, I'm seeing three separate photos that clearly show the power cord. And, only three wires from it....brown, blue, green (chassis ground). In the first photo (earliest post), the blue is tied to orange and off to the side of the cap. However, in the following post, I see the blue/orange wires tied to the positive terminal of the cap?? (Let's just ignore the hanging white wire for now.) (Specifically, look at the power cord wiring in post 47)

So, at one point, the 240vac feed was literally tied to the B+ cap? It's no surprise everything was going up in smoke. I'd be replacing all those caps and a whole lot of testing needs to happen. Like Pete referenced regarding the caps venting...at least now it's no surprise why.

If you were just smoking caps, you may have got lucky with the PT...the alternating voltage likely cooked the caps without exceeding the current draw for blowing the fuse. Either case, please don't just 'replace parts'...get it to a tech with the proper equipment to ensure nothing else is compromised you can't see (or smell??? lol)

Good luck!
Brad

what does 15 amps do to diodes? if it shorted them ( have they been replaced?) then the secondary winding designed for a couple of hundred milliamps saw 15 amps. bye bye secondary h.t winding

 

[neikeel]

I raised those issues is post number 43