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Old 1st April 2008, 06:28 PM   #1
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Default Transformer repair

I'm trying to salvage set of vintage transformers that I have, but I'm not sure if it's a good idea or not. These guys are roughtly 1959 vintage, very heavy and look to be decent quality. The problem: the power transformer windings are wrapped in paper which is crumbling and the insulation on the leads are also very crumbly.

The OPT's seem OK, and if I'm careful should be alright as-is. The power transformer on the other hand probably isn't safe anymore. I've taken off the end bells and more crumbling! The E/I stack appears to be lacquered together.

Salvageable or scrap metal?

If it can be saved, anyone suggest any reading?

I've found some possibly applicable reading, but it doesn't deal with EI core winding: http://www.users.on.net/~endsodds/tx.htm
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Old 1st April 2008, 07:32 PM   #2
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After reading your description of crumbling paper insulation, my first thought is to recommend trashing it. But it really all depends on just how bad off it is.

I salvaged a power transformer once years ago that had cloth leads that were dried out and crumbling, but the winding insulation was not too bad. I was lucky enough to have the type of transformer construction where the wires were all connected to the windings at the outside level or top of the winding build.

I carefully removed the outer layer of covering from around the coil body untill I could see the lead connections and how they were soldered to the windings. This was done with the steel core intact.

The winding wires were twisted and soldered to the leads in a row with a thick piece of fish-paper underneath them which served as a base and protection to the windings below. I kept this thick piece in place. And after installing new wire leads by re-twisting and soldering them as they were before, I covered this area with a piece of 10kv insulating cambric that I had and was available at most electronic supply houses at the time. (probably still is)

To finish things up I wrapped the entire coil with insulating tape by passing it through the window in the core and pulling it tight. I think I used black electrical or firction tape. (can't remember) But do not use masking or package sealing tape since it won't take the heat of operation. Today I would probably use kapton tape or one of the high voltage tapes available that I didn't have then.

The decision you have to make is if the winding insulation is good enough to try doing something like this. If it's really crumbling badly, then I say no, don't use it for safety reasons alone.

The core is of little value unless you want to experiment winding a transformer from scratch. The laminations will come apart by using a knife edge and hammer to begin separating them at a corner. The first couple of laminations are the hardest to get apart because they are probably very tight in the windings. There may even be a wood wedge under the coil body to keep it tight on the steel.

Good luck,
Victor
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Old 2nd April 2008, 01:59 AM   #3
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Quote:
Salvageable or scrap metal?
If the windings check out ok, and insulations between windings are fine, and if you can use those on a project, then i'd say salvage them.

to protect the windings, you can use "Fula-tite" or poly-tuff, these are polyester resins you can use. they're are used for car painting and repairs, i use them a lot on big transformers.

they can be sanded/machined and made to look like end-bells after they hardened..
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Old 2nd April 2008, 01:24 PM   #4
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Thanks for everyone's input!

I took a closer look at them last evening. I think they are salvageable. One side seems to be stable, and only one layer has crumbled off on the other. The paper inserts that were on the sides of the windings also crumbled out. So I'm thinking if I replace the leads, and then seal the troubled side with some insulating goo or tape, I may be good to go. The sides will need some sort of plastic or paper insert as well.

My guess is that the host amplifier sat on someone's basement or garage floor and it got wet on the bottom. There were signs of water exposure all inside the old thing. Old paper don't like water.
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Old 2nd April 2008, 03:32 PM   #5
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Any trannie that has been in water for any period of time is bad news! If you have any doubts about it, you can take it to a professional transformer person for his opinion. You definitely don't want to start a fire!
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Old 2nd April 2008, 03:59 PM   #6
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It sound's worse than it is. It worked fine until I pulled it from the amp's chassis.
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