Re: 547 HV Transformer: Bill Schell rewind failed


Talked to Bill Schell a couple of decades ago about taking over and buying his setup from him.Instead, I ended up contributing what I had learned to Chuck Harris' efforts.My recollection is that Bill did NOT use epoxy, but potted in straight beeswax.Chuck and I discussed this at length, considering beeswax vs paraffin.Chuck tested 10 mixtures and found best dimensional stability with a mixture of both.
I suspect incomplete impregnation or less than ideal coil pack resulting from his scatter winding method.Never heard of a Schell rewind failing until now.Bernie Schroder

-----Original Message-----
From: Dave Wise <>
To: <>
Sent: Wed, Mar 3, 2021 8:06 am
Subject: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

In 2017, my 547 with Bill Schell HV transformer (installed around 2000) was working.  It has sat unused in a dry basement since then.

Today, in March 2021, that transformer exhibits the same thermal runaway symptom as the original Tek part.  (Fades out in ten minutes.)

Hours of warming have not restored it.  I don't think it will.  I used to think my Bill Schell transformer was wax-impregnated; now I don't.  I think it's epoxy, and like Tek's, it has gone bad.

I hope other Bill Schell customers can check in with their status.

I have an ace in the hole.  In my drawer is... a 2010 Chuck Harris rewind.  To ice the cake, it's the one Stan Griffiths was evaluating - he gave it to me after he was done with it.  I'll install it soon.

Dave Wise

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