Transformer potting

[bikerhifinut]

Has anyone here any experience of this?
I have a pair of large(ish)mains transformers that I'd like to pot up as a last ditch attempt at reducing the noise from the windings. Its not practical to suggest a rewind, I'd get a new pair made for the same or less. Neither is it worth any futile suggestions on impregnation as the offending winding is buried under layers of secondaries. I've had them examined by a transformer expert, whom I trust completely and his diagnosis was that the primary had not been wound tightly enough to the former and thus it was never going to be silent or quiet.
Now since I started running them at the correct 230V by dint of a homebrew autotransformer/bucking arrangement they do run quite cool and so I should be ok to use a thermally conductive potting compound.
So I need a container to pot them in and some compound.
Any help or suggestions? I'm no good at metal fabrication so please no "buy a sheet of metal and bend it" stuff unless you know of a good inexpensive workshop who could make me one. I was advised by someone that an ABS type box could work but my feeling is a thermally conductive substance eg metal would be better.
This is a last ditch attempt at silencing what would otherwise be scrap as a mechanically noisy mains transformer has no place in a hi fi amplifier.

Andy.

[bob orbell]

Difficult one Andy, I have only potted SUT's, so, not too sure about power joby's, if you give me some dimensions of the size and shape of the pot's you have in mind, I can ask at our local tin shop,I may be able to get it / them made and out of the back door, , but can't make any promises. I will answer your PM latter. One more room to do by the way. BOB. still covered in paint.

[bikerhifinut]

Thanks Bob.

Andy.

[John Caswell]

Hi all,
If you can get a suitable can made, that you can seal, how about oil filling?
It does have the advantage of getting in everywhere, and if you cook it in the oven, a lot of the air will be driven out. Not sure where you would get the oil though!
Just a thought

John

[bikerhifinut]

I spoke to the manufacturers today and they were of the opinion that epoxy potting the mains transformers might make the vibration issue worse.
So maybe it's not the way to go.
I'm bitterly disappointed and its made me wary of getting transformers wound in the future as this is the second manufacturer that seems incapable of winding a silent running power transformer.
I did have them checked by a proper transformer expert of my acquaintance and his verdict was fairly damning in respect of the way the primary was wound and that the impregnation wouldn't have made it into the windings. They are only hot dipped in varnish anyway, not as I thought vacuum impregged.
So I'm weighing up my options.

Andy

[pre65]

Are these transformers Toroidal ?

[bikerhifinut]

Philip,
No they are bog standard E I jobs. Anyway they are substandard and there's an end to it. Life's too short to keep chasing wild geese.
You wouldn't varnish impreg a toroid anyway surely?
Andy.

[Greg.]

I don't know if this safe or even right but I have read about others enhancing absorption of vanish into the windings by submerging in vanish and then heating in a pressure cooker.

[bikerhifinut]

I suppose its a sort of inverse vacuum impregging Greg?
Waste of time on these, Mike (BVWS Thransformer guru, I think you know who Imean) has inspected them physically for me and basically they are poorly wound therefore a lost cause.
They work fine in as much as they deliver the Volts and amps as designed and run cool if fed 230v AC rather than our normal 250 to 253 (legal limit) mains.
But too mechanically noisy for a Hi Fi amp.

[Richard]

Yes Paul Barker was telling me of a similar method with the pressure cooker and, I think, a small amount of water which was allowed to cool and condense causing a vacuum (when the valve hole was blocked?). I've probably got this around my neck, it was at least 10 years ago, but you could drop him a message over on Audio Talk to see if he can help