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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 5th Jul 2020, 12:31 pm   #1
Gabe001
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Default Transformer delamination

As some of you may have known from my previous posts, one of my radios, a pilot u650, had a buzzing transformer. Not much, but it got to me. Having had enough of tightening and loosening the transformer tappings to try to get on top of things, which improved things temporarily, I decided it was time for a more permanent solution.

Taking inspiration from the practice of dipping transformers in shellac, I bought insulating transformer dipping varnish from a well known electric components supplier.

After loosening the transformer screws and nuts to allow the transformer to be lifted slightly off the chassis and get a few millimetres of space between the loose laminates (in my case the 3 at the bottom), I injected the varnish carefully between these laminates using a syringe and plastic cannula (from an e bay kit to repair wallpaper). It was slow going and due to the thickness of the liquid. I then pained the outside of the transformer laminates using the same varnish, and re-tightened the transformer screws and bolts to the case

After letting it dry for 48 hrs the transformer seems to be completely silent. Hopefully this will last.

Just posting in case it helps someone. Dipping would probably also have worked I'm sure but I'm not so confident of my skills to feel comfortable completely removing and reattaching a transformer.

KR,
Gabriel
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Old 5th Jul 2020, 1:04 pm   #2
Radio Wrangler
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Default Re: Transformer delamination

The best varnish impregnation uses a vacuum chamber, but some people have built their own. The idea is that the transformer windings and lams will out-gas their voids, and when varnish is added and the thing brought up to atmospheric pressure the vacuum in the voids will suck in varnish.

I had the devil of a job quieting some big toroids. Two dunks of vac-impreg helped but I ended up casting them in silicone.

David
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Old 5th Jul 2020, 1:20 pm   #3
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Default Re: Transformer delamination

I have a Digimess (what a name) power supply that hummed awfully, I filled the toroidal transformer "hole" with car body filler quite liberally (it looks a bit of a mess). Ah, silence.

Car body filler is a very cheap filler/adhesive one should keep in stock. Sets in a few minutes (you can hold bits in place by hand during the setting) and after a couple of days it is sticking very well indeed.
 
Old 5th Jul 2020, 2:16 pm   #4
turretslug
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Default Re: Transformer delamination

Good outcome there Gabriel, yes, transformer buzz can be a bit of a bug-bear when everything else about a piece of electronics is working great, and there can be an element of "gotcha-no-you-haven't...." about it. I'll remember those tips,

Colin
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Old 5th Jul 2020, 6:58 pm   #5
Ed_Dinning
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Default Re: Transformer delamination

Hi Gents, be careful not to overdo it as the transformer may then overheat, not being able to pass out the excess heat to atmosphere

Ed
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Old 12th Nov 2020, 6:06 pm   #6
Gabe001
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Default Re: Transformer delamination

Just to report back that after a period of silence it started buzzing again, not as much as before but unfortunately still there in the background. Damn!

I'll be looking at replacing the transformer in due course, most likely one from primarywindings + bridge rectifier (like for like will be too expensive), as I've had enough now. I'll use the opportunity to do some rewiring which I think is overdue.

Anyway, varnish doesn't work unless applied in a vacuum, lesson learnt.

Gabriel
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