Re: 547 HV Transformer: Bill Schell rewind failed

Chuck Harris <cfharris@...>

Hi Tom,

Moisture is definitely a factor, but the problem is not
really reversible.

Yes, you can gain an improvement by cooking, or vacuum
drying, a tektronix epoxy transformer, but it will return
to its failed condition in a much shorter time than it did

My guess is the brownish/red coloration to the epoxy is
because tektronix added a fire retardant to the epoxy...
most everyone did back then, resulting in a lot of failures
over the years. One place you hear quite a lot about it is
in red doorknob style epoxy molded HV capacitors.

Time has showed that the bromine, and other fire retardants,
have failed in a variety of ways everywhere industry used

Fire retardant plywood loses its structural integrity after
about 10 years, causing roofs to collapse. Fire retardant
added to plastic computer and monitor enclosures caused
them to turn brown over time... and let's not forget about
tris added to kid's pajamas!

-Chuck Harris

fiftythreebuick wrote:

Hi Dave-

I'm sorry to hear that you're having trouble with that HV XFMR....

I did a lot of testing and evaluation for Bill Schell over the years and I don't remember him every testing a transformer with any epoxy in it at all. He and I both felt that we oughta get as far away from that as possible. He first wound them without sealing them and I have never had one of those fail. Then when he started treating them with beeswax and a vacuum chamber, it seemed like he had found quite a good process. So far, I have never had one of his fail, of any description.

Just saw your later post and I'm glad that yours is improving! A friend of mine has restored an original xfmr by putting it in a vacuum chamber and keeping it in a deep vacuum for a while. Don't remember how long he left it in there.

I hope yours comes out alright. It really does seem like the moisture is the major factor.


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