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donnyab 3rd December 2011 11:15 AM

potting transformer enclosures
 
Hi,
I want to start winding my own audio transformers, if anyone else doing the same do you have a source for steel enclosures of appropriate size etc.
I am based in UK but will buy from anywhere, not necessarily have to be powder coated or enameled either.
Also older types with steel lid/base etc are fine, they don't have to look like Tango enclosures.
The best I can find are steel utility boxes from Hammond which are not air tight [plan on using paraffin wax].
Thanks

pieter t 3rd December 2011 02:05 PM

Maybe you find here something to your liking:

cubesfortubes.de

lakeside 3rd December 2011 02:34 PM

These guys have a few.
Transformer cover

jlsem 3rd December 2011 06:18 PM

Quote:

Originally Posted by donnyab (Post 2804619)
Hi,
[plan on using paraffin wax].
Thanks

This is more suitable for potting transformers:

10 LBS Microcrystalline Wax / Sculpture Wax / Encaustic | eBay

John

Mark Allen 3rd December 2011 11:26 PM

I think one would want to use an epoxy potting compound or similar. Older wax and tar filled transformers tend to drip badly do to the heat build up from being in an enclosed environment.

Mark

gorgon53 4th December 2011 02:09 AM

For PS-toroids i used sometimes aluminium cattles with the bolted on handle removed. With some luck you can find suitable good looking teflon coated ones. Cast iron would be great but i never stumbled over suitable ones . Bottom down mounted cattles can be filled with tar or wax . Would be nice to have all the necessary data to be able to choose the best suitable filling compound , but this is the hardest part. Dielectric properties are mostly unknown but they can have a big impact on a audio transformer. Some epoxies and urethanes are suitable for PST. For a audio-transformer i would avoid potting (if possible) or use at least beewax with known properties.

AmpliFire 4th December 2011 09:06 AM

Quote:

Originally Posted by lakeside (Post 2804842)
These guys have a few.
Transformer cover

Thanks! That's a very interesting supplier !

donnyab 4th December 2011 10:25 AM

Thanks for replies, the German ones look good albeit a bit on the expensive size.

[I have also come across small steel galvanized boxes used in the electrical industry *nema 3R rain tight boxes* that look promising, although they may have hidden holes in inconvenient places.]

pieter t 4th December 2011 11:19 AM

Quote:

Originally Posted by gorgon53 (Post 2805611)
Would be nice to have all the necessary data to be able to choose the best suitable filling compound , but this is the hardest part. Dielectric properties are mostly unknown but they can have a big impact on a audio transformer. Some epoxies and urethanes are suitable for PST. For a audio-transformer i would avoid potting (if possible) or use at least beewax with known properties.

Not quite agree.
As written before here in the first place there is impregnating and potting, which are different.
When impregnating, the material is supposed to impregnate the coil, preferably under vacuum, and finished by drying or heating depending on sort of material. This is good practice for power supply transformers and chokes, and not so good practice for audio transformers because of dielectric properties.
Potting is filling an enclosure, with the transformer in it, with some sort of compound. Epoxy or poly-urethane based compounds are mostly used for this (in earlier days tar was used).
When potting an accurately wound (interleaved) audio transformer the dielectric properties actually don't get worse (the potting compound will not get into the coil). I measured this.
Potting can even be beneficial for audio transformers as these can be microphonic.

donnyab 4th December 2011 12:23 PM

Probably won't try to pot them now anyway.
I don't have the facilities to vacuum impregnate a winding so that is why I was thinking of using wax. If I use wax though as has been said it may be detrimental to the sound as molten wax would definitely get into the windings. I thought the wax may have had a beneficial effect in terms of dampening the vibrations in the windings etc. Maybe that is not needed at all if they are wound tightly enough ?
I just bought two Lundahl output transformer last week and the windings are not varnish impregnated.


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