Re: 547 HV Transformer: Bill Schell rewind failed

Dave Wise

Chuck, your transformer worked great in 2010. A note reads that 6AU5 screen voltage was about 45V, and stable. That's way better than new.


With the intensity control at its original position, the trace is approaching original brightness.

My long-term-idle Bill Schell transformer is responding to baking.

Dave Wise

From: <> on behalf of Chuck Harris via <>
Sent: Wednesday, March 03, 2021 9:47 AM
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

Hi Dave,

That is interesting, as I never sold any transformers to Stan.

So, did I pass muster?

-Chuck Harris

Dave Wise wrote:

I retract my doom and gloom. Further warming seems to be restoring it after all. I simply left the scope running, with the intensity control at a safe position. I don't have a visible trace yet but as time passes I have to advance the control less and less to get one.

This data point corroborates the theory of moisture-ingress or other reversible reaction.

I will report back later.

Dave Wise

Note: This 547 has the 6AU5 screen grid voltage limit mod.

From: <> on behalf of Dave Wise via <>
Sent: Wednesday, March 03, 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

Join to automatically receive all group messages.