Compromised PT

[lowell]

This Trace Elliot GP12SMX whacky amp came in with the outer windings of the PT insulation scratched off. Apparently someone was poking a screwdriver thru the missing speaker jack hole for some CRAZY reason. Not to mention a slew of other weird issues. Customer said a friend tried to fix it but obviously did more damage than repair. Anywho, picture attached, IMO this PT is quite dangerous and should be replaced. Would like some feedback on whether it's possible to add electrical tape around the outside of the transformer. If the windings aren't shorted, would this be suitable or should I in no way considering using this PT? My gut says JUST SAY NO

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[The Dude]

Wow! Somebody's a smart one!

At first glance, I was thinking no way would I use that. Then I blew up the picture as big as I could and it appears that damage is between actual windings. Of course that's from a picture on a computer. You have the thing in front of you, so it's obviously best you inspect it yourself. Make sure no actual wires have been dug into, coating scratched off, etc. If it is salvageable and still works, I would refill the parts "dug out" with an insulator. Maybe silicon? (someone here will likely have a better idea), before you just cover it up. Again, take this with some salt- it's hard to tell for sure just looking at a picture. There's also that big hole in the middle. How deep does it go? Does the transformer still work?

[mozz]

Put some of that high voltage shellac in there, insulating varnish made by GC.

[lowell]

There is indeed insulation scratched off. Can you zoom in at all? I see bare copper. So, I don't know how these are wound... could the very outer part be just one winding or is it likely that more than one winding is adjacent to another? i know some transformers are wound together, in parallel, and some not. The bulb limiter seems ok when I power on, but without it I fee arcing, expecially when LOUD bass is being played thru it.

[nosaj]

This Trace Elliot GP12SMX whacky amp came in with the outer windings of the PT insulation scratched off. Apparently someone was poking a screwdriver thru the missing speaker jack hole for some CRAZY reason. Not to mention a slew of other weird issues. Customer said a friend tried to fix it but obviously did more damage than repair. Anywho, picture attached, IMO this PT is quite dangerous and should be replaced. Would like some feedback on whether it's possible to add electrical tape around the outside of the transformer. If the windings aren't shorted, would this be suitable or should I in no way considering using this PT? My gut says JUST SAY NO

[ATTACH=CONFIG]41996[/ATTACH].

Go with your gut and sidestep the liability. Quote a PT.

nosaj

[olddawg]

As mentioned before....I would try a couple of coats of insulation varnish witha brush. AND it would plug that hole so it doesn't happen again. If it works. I would run it a couple of days on a load bank before releasing it AND tell the customer exactly what you did and why.

[Randall]

No way in Hell I would try to fix that without replacing the PT. Is it possible? Maybe. Is it smart? No. You try to fix that PT and something goes afoul down the road, you are liable as the last one to work on it.

[Justin Thomas]

I think it was a typo, but if "I fee arcing" was supposed to be "I see arcing" then I wouldn't trust it... my amp? I'd try to fix it. Customer amp? I'm with Randall - liability too big. Replace it, AND tell them not to let their "friend" work on their amps ever again. Of course, if the customer doesn't want the old part, have some fun!

Justin

[The Dude]

Oh yes, if you see arcing, it's got to go.

[Chuck H]

AND tell them not to let their "friend" work on their amps

Or any one else's amps. Or anything flammable. Or anything that involves food preparation. Or practice child care. Or give traffic directions, etc., etc.

ever again.

[The Dude]

[olddawg]

Oh yes, if you see arcing, it's got to go.

Of course if the part is easily available and the repair can be done for what the owner is willing to pay, the transformer should be replaced. If you can't get the part or it's prohibitively expensive, I wouldn't trash the amp because of a little missing lacquer. Unless someone gets inside of the amp again, I don't see what the big "liability" is? A blown fuse? I've repaired transformers like this before (and worse, lol). People want their stuff back working and they usually want a quick turnaround. You are just replacing a little bit of missing lacquer. It will either work or it won't.

[R.G.]

In most toroidals like this one, the outer winding is the secondary. I'm guessing that this one is that way, as the wires are wound in pairs, the correct way to wind a center tapped winding. You could check the winding leads to the bare copper spots there and tell. That would let you know if the exposed copper is primary wire or not.

If the exposed copper was primary, I would tell the owner that no way I'd work on it without replacing the transformer. Too dangerous to him and anyone who comes after him (and you!) with that amp.

IF the winding is secondary only AND IF no other insulation to the primary has been compromised AND IF the windings are still conducting and not shorting, it could be made to work for a few times, as in show-must-go-on-and-I'll-risk-anything-to-do-it situations. Since it's in your shop, I'm guessing that does not apply.

The transformer's long term life has been compromised even if it kinda works now. Any varnishing, pasting, or soaking in eye of newt stew is merely publishing the illusion that everything is OK now.

I'd replace the trannie unless it just can't be replaced for some reason. If it can't be replaced, have someone rewind it.

[R.G.]

Forgot to mention - scraping the varnish off the wires nicks the wires there too, and forms a spot which gets hotter than the other wire around it, as well as making it prone to stress cracks right there. Transformer vibration from mechanical hum can do the rest.

[The Dude]

I think this should be the one.

British Audio Service & Music