I'll second that.

Varnish is the best thing. Warm the varnish and the
transformer first before you dunk it. That will reduce
the viscosity and improve penetration. A little thinner
in the pot may help too. Vacuum/pressure impregnation is
better than dipping... but dipping can work well on a buzz.

There is even special dipping resin to reduce noise that
leaves the part looking like it's been dipped in a candy
coating. It's a soft, rubbery, epoxy coating.

Oh, and the teflon isn't so great as a shim. You might try
nomex paper, G-10 PC board scraps, fish or kraft paper even
typing paper, calendered cardboard (like shoe box cardbord)
or wood. Teflon will withstand the heat but it tends to
cold flow which makes it dimensionally unstable. The amount
of mechanical force between the core halves can be surprising.
Though in your transformer teflon may be be OK. In a choke
it can be a source of bewilderment as the gap decreases. Yes,
I've had this happen.

Any material that will soften when it's hot, like perspex/plexiglas
isn't a good choice either. I found this in an inductor for a
10KW boost converter that an otherwise reliable supplier built
for me.

For varnish, I like Dolphs (Von-Roll.) Failing that I use
marine spar varnish. Some varnishes are corrosive to copper
and over time will cause windings of fine guage to open if
any copper is exposed.




ken scharf wrote in
:

I've sealed rewound filter chokes by dipping them in a bucket of
polyurethane varnish.