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547 HV Transformer: Bill Schell rewind failed
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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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?Update.
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: [email protected] <[email protected]> on behalf of Dave Wise via groups.io <david_wise@...> Sent: Wednesday, March 03, 2021 8:06 AM To: [email protected] 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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widgethunter
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.
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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 <david_wise@...> To: [email protected] <[email protected]> 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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On Wed, Mar 3, 2021 at 08:06 AM, Dave Wise wrote:
Hi Dave: Sorry to hear about your trouble. Perhaps you don't remember... because the last time you handled the transformer was when you installed it... but, how does one mistake wax for epoxy?... or vice versa. |
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?Roy,
I uploaded pictures to album "?547 HV transformer rewind by Bill Schell". Tell me what you think. Dave Wise Update: Still improving; the intensified part of the trace is now visible at the original intensity setting. ________________________________ From: [email protected] <[email protected]> on behalf of Roy Thistle via groups.io <roy.thistle@...> Sent: Wednesday, March 03, 2021 8:47 AM To: [email protected] Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed On Wed, Mar 3, 2021 at 08:06 AM, Dave Wise wrote: Hi Dave: Sorry to hear about your trouble. Perhaps you don't remember... because the last time you handled the transformer was when you installed it... but, how does one mistake wax for epoxy?... or vice versa. |
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Chuck Harris
Hi Dave,
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That is interesting, as I never sold any transformers to Stan. So, did I pass muster? -Chuck Harris Dave Wise wrote: ?Update. |
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Chuck Harris
Hi Bernd,
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There have been several discussions about Bill's transformers of late, and there is a picture on the group, that looks very much like epoxy varnish, or some other non wax compound. However, it is most definitely not scatter wound. It is a nice looking, self supporting, universal wind. Bill didn't use an outer tape covering on this transformer. The naked winding is right there for you to see. -Chuck Harris widgethunter via groups.io wrote: 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. |
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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.
Update. 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: [email protected] <[email protected]> on behalf of Chuck Harris via groups.io <cfharris@...> Sent: Wednesday, March 03, 2021 9:47 AM To: [email protected] 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: ?Update. |
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?Chuck, I think *I* bought that transformer from you - just to have a spare on hand - and loaned it to Stan for evaluation. Since my Bill Schell was happy, I wouldn't have swapped it out.
Dave Wise ________________________________ From: [email protected] <[email protected]> on behalf of Dave Wise via groups.io <david_wise@...> Sent: Wednesday, March 03, 2021 11:24 AM To: [email protected] Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed 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. Update. 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: [email protected] <[email protected]> on behalf of Chuck Harris via groups.io <cfharris@...> Sent: Wednesday, March 03, 2021 9:47 AM To: [email protected] 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: ?Update. |
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?Roy, your signature is not included in the groups.io footer. Thanks for including your name in the message body.
Dave Wise ________________________________ From: [email protected] <[email protected]> on behalf of Roy Thistle via groups.io <roy.thistle@...> Sent: Wednesday, March 03, 2021 11:33 AM To: [email protected] Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed Hi Dave: Thanks for the reply... I'll check it the pic. Hi it's Roy ( I'm a bit confused as.... usually.... if one doesn't address the O.P. directly by name... one is talking to the group... maybe that's not the convention? ) Also, I thought my "signature" in the footer was appearing? |
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Chuck Harris
Hi Dave,
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I have long believed that the reason there were so few failures with beeswax HV transformers is "wet" beeswax will get hot and melt, letting the water out. Because the windings are so close together, they act like a sponge, and as long as the beeswax isn't made to boil, its surface tension should keep it in the coil... It shouldn't drip everywhere. -Chuck Harris Dave Wise wrote: 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. |
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On Wed, Mar 3, 2021 at 01:19 PM, snapdiode wrote:
It didn't run for more than 30 minutes, and then failed ... or you didn't run it for more than 30 minutes? .... and then you turned it off. (In which case the working state is unknown.) |
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Just another flashlight probing the darkness...
Back in December I received some mis Tek goodies from a kind member of the "Old Tek Scopes" Facebook group,.. some obviously appearing to be HV transformer rewinds. One has the hand written notation on the tape holding the core halves: "0308 6-6-94 W.A.S." (could be W.R.S.) on one side, "Either 547 or 454 Good" on the other This specimen has what appears (by fingernail test and sight) to be a beeswax coating. Defiantly not epoxy. The wind job also looks to be a professional universal, and hasn't been put to use since re-manufacture. -Roger |
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?Update.
This morning it ran for an hour maintaining normal brightness. I think it's healed. I guess it absorbed moisture over the four years it sat, and yesterday I baked it out. I can't explain why it didn't become lossy during other years-long idle periods between 2003 and 2017. Carry on. Dave Wise ________________________________ From: [email protected] <[email protected]> on behalf of Roy Thistle via groups.io <roy.thistle@...> Sent: Wednesday, March 03, 2021 2:58 PM To: [email protected] Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed On Wed, Mar 3, 2021 at 01:19 PM, snapdiode wrote: It didn't run for more than 30 minutes, and then failed ... or you didn't run it for more than 30 minutes? .... and then you turned it off. (In which case the working state is unknown.) |
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widgethunter
Hi Chuck;Assumed scatter because of the larger size of Schell rewinds.It has been a looong time, but I think I'd remember if he'd said anything about epoxy...B
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-----Original Message-----
From: Chuck Harris <cfharris@...> To: [email protected] Sent: Wed, Mar 3, 2021 9:57 am Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed Hi Bernd, There have been several discussions about Bill's transformers of late, and there is a picture on the group, that looks very much like epoxy varnish, or some other non wax compound. However, it is most definitely not scatter wound.? It is a nice looking, self supporting, universal wind. Bill didn't use an outer tape covering on this transformer.? The naked winding is right there for you to see. -Chuck Harris widgethunter via groups.io wrote: 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. |
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Roger:
If's beeswax (It could be paraffin wax, or a silicone wax, or some other wax type potting...or not even wax) If it's beeswax... and you want to verify... put a tiny scraping of it in a spoon, and hold it in the steam of a boiling kettle... it will soon melt. Also, beeswax has a pleasant fragrance. -- Roy Thistle |
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Chuck Harris
Hi Bernd,
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I guess the biggest indicator of a scatter wind would be the presence of a spool. The universal wind doesn't require any additional support. In addition to talking to you, I talked to Deane Kidd, and Deane talked about Bill using beeswax, like tektronix did in the earlier transformers. But, like you, it has been a looong time, and I don't think our memories are getting any better. -Chuck Harris widgethunter via groups.io wrote: Hi Chuck;Assumed scatter because of the larger size of Schell rewinds.It has been a looong time, but I think I'd remember if he'd said anything about epoxy...B |
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