potting transformer enclosures

[donnyab]

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]

Maybe you find here something to your liking:

cubesfortubes.de

 

[lakeside]

These guys have a few.
Transformer cover

 

[jlsem]

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]

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]

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]

These guys have a few.
Transformer cover

Thanks! That's a very interesting supplier !

 

[donnyab]

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]

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]

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.

 

[gorgon53]

Good to know that modern potting materials wont enter a conventionally wound coil. I was a bit hasty by abonding potting alltogether and did not take into account that most transformer are still wound with solid isolation between layers.
I never measured, but i tried to take some potted transformers apart and they always where to at least 50% soaked and glued together with tar or wax .
I hope I will find a way to prevent the potting material to enter my coils but i do not want to go back to standard winding technices. I either perforate solid isolation material or use solid material only at the edges. This way a average Dk below 1.2 is achievable.
Because of this pain in the *** winding technic potting would be very wellcome to protect those coils. Microphony is no issue for me since i have to use bonding wire and/or glue to keep those coils together.
But still, sufficent data about the properties of all sorts of isolation, potting, glue a. s. o. materials would be wellcome.