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I would concur but bake the transformer in an oven first to drive out
moisture, and heat the whole thing - soak at ~200 F for a few hours.
Then dip the hot transformer in varnish and suspend it for a minute or
two in the pail. Let cool in a warm dry place. The transformer
retains enough residual heat to have the varnish set quickly.
The heat thins the varnish and as the laminations and coils cool, the
air contained in the interstitial spaces contracts and sucks in
varnish.
If one is really going to get into the business of winding 60
hertz/audio transformers, a flea market quality pressure cooker or
canner can become a vacuum oven/impregnator.
I wound a large induction coil and used a pressure cooker to vacuum
impregnate it with hot paraffin wax - worked like a champ.
Right now I'm building some coils on a winder with a chilled epoxy
coating - the mandrel is non-stick polyethylene with a light oil
coating and the finished coils look superb.
