Moved Here - Type 547 HV Transformer Repair

[Zenith]

I suspect you are stuck with rewinding that transformer, or buying a replacement from someone geared up to do it.

Have you seen this?

https://w140.com/tekwiki/wiki/HV_transformers

There's a link on it to a document on rewinding Tek transformers. It goes into great detail on the windings and core materials etc, but only mentions potting in passing. He mentions a two component resin. No talk of vacuum chambers or ovens.

[Cerebus]

I’d recommend against using the microwave to try to dry a transformer…

I need to dig out the vacuum chamber I got last year.

-Pat

most guys casually buy things like toaster ovens.

seems like cub runs out to the dollar store and comes home with a vacuum chamber?

I have two toaster ovens, one for food and one for electronics. I also have a Javac DD300 vacuum pump (ultimate vacuum 0.5 ubar/0.05 Pa/0.04 mTorr) but haven't yet got around to getting the plumbing or a chamber to go with it.

[tggzzz]

I’d recommend against using the microwave to try to dry a transformer…

I need to dig out the vacuum chamber I got last year.

-Pat

most guys casually buy things like toaster ovens.

seems like cub runs out to the dollar store and comes home with a vacuum chamber?

I have two toaster ovens, one for food and one for electronics. I also have a Javac DD300 vacuum pump (ultimate vacuum 0.5 ubar/0.05 Pa/0.04 mTorr) but haven't yet got around to getting the plumbing or a chamber to go with it.

I have N saucepans, N-1 for cooking, and one for reflowing SMD boards

[Cubdriver]

I’d recommend against using the microwave to try to dry a transformer…

I need to dig out the vacuum chamber I got last year.

-Pat

most guys casually buy things like toaster ovens.

seems like cub runs out to the dollar store and comes home with a vacuum chamber?

the amazing thing is that he probably has two of them........but one is forgotten behind his liquid scintillator neutrino detector......and then he WILL post pictures of the vacuum chamber with a kitten napping inside.

Nope, I only have the one. Bought it from either Slamazon or the Bay of Malevolence a year or two ago when we first started talking about failing 547 HV transformers, with the intent of trying to dry mine in it when it got to that point. The 547 has since moved back in the queue, and I need to rebuild my bomba de vacío as it has been piddling pump oil on the ground, so the chamber is still sitting in its box on my kitchen floor. No doubt kitties have napped upon it, but none have yet been inside.

I can however include a 'cat with a counter' picture.


-Pat

[MED6753]

I suspect you are stuck with rewinding that transformer, or buying a replacement from someone geared up to do it.

Have you seen this?

https://w140.com/tekwiki/wiki/HV_transformers

There's a link on it to a document on rewinding Tek transformers. It goes into great detail on the windings and core materials etc, but only mentions potting in passing. He mentions a two component resin. No talk of vacuum chambers or ovens.

Thanks for the info. I quickly browsed the document but one thing immediately caught my attention. He stated that the failure is caused by overheating. First time I heard that. The consensus among the Tek community is that the failure is caused by moisture absorption by the epoxy potting. And it appears that my ongoing experiment here pretty much proves that. Would baking out the transformer cure an overheating problem, even on a temporary basis? I kinda doubt it. And the load (and potential overheating) is further alleviated by removing the 5642 vacuum tubes and installing silicon rectifiers thus eliminating the filament load. Now maybe....just maybe....that the moisture absorption leads to overheating. I suppose that's possible. But until proven otherwise I'm sticking with eliminate the moisture and you cure the issue. For now anyway.

I also didn't see any mention of the potting he used but I'll read the document in more detail. That's an important part of rewinding the transformers.

[Cerebus]

..., so the chamber is still sitting in its box on my kitchen floor. No doubt kitties have napped upon it, but none have yet been inside.

I'm rather surprised that you haven't been hauled before the Kitty Council for crimes again catkind: wilful and knowing possession of an unopened box contrary to the Universal Declaration of Cat Rights (implementation) Act. It's a slam dunk case, and I hear the penalties are severe.

[Specmaster]

..., so the chamber is still sitting in its box on my kitchen floor. No doubt kitties have napped upon it, but none have yet been inside.

I'm rather surprised that you haven't been hauled before the Kitty Council for crimes again catkind: wilful and knowing possession of an unopened box contrary to the Universal Declaration of Cat Rights (implementation) Act. It's a slam dunk case, and I hear the penalties are severe.

LMAO

That reminded me of this cartoon.

cathouse.jpg

[Zenith]

I suspect you are stuck with rewinding that transformer, or buying a replacement from someone geared up to do it.

Have you seen this?

https://w140.com/tekwiki/wiki/HV_transformers

There's a link on it to a document on rewinding Tek transformers. It goes into great detail on the windings and core materials etc, but only mentions potting in passing. He mentions a two component resin. No talk of vacuum chambers or ovens.

Thanks for the info. I quickly browsed the document but one thing immediately caught my attention. He stated that the failure is caused by overheating. First time I heard that. The consensus among the Tek community is that the failure is caused by moisture absorption by the epoxy potting. And it appears that my ongoing experiment here pretty much proves that. Would baking out the transformer cure an overheating problem, even on a temporary basis? I kinda doubt it. And the load (and potential overheating) is further alleviated by removing the 5642 vacuum tubes and installing silicon rectifiers thus eliminating the filament load. Now maybe....just maybe....that the moisture absorption leads to overheating. I suppose that's possible. But until proven otherwise I'm sticking with eliminate the moisture and you cure the issue. For now anyway.

I also didn't see any mention of the potting he used but I'll read the document in more detail. That's an important part of rewinding the transformers.

I vaguely recall I read somewhere that the moisture increases losses and causes overheating. Maybe. I suspect it's speculation rather than the result of a rigorous investigation.

I think you have two possible approaches.

Bake the transformer to remove all moisture and pot it with the existing potting in place, that is additionally pot it.

Wind a new transformer (and his instructions seem worth following), bake it and pot it.

Either involves a suitable oven and vacuum chamber to get rid of the bubbles, plus a potting compound appropriate for high voltage transformers. A domestic electric oven (not gas) might do for the first. Possibly putting the transformer in an airtight container with silica gel (or better dessicant) would get rid of the moisture. Vacuum chambers for degassing urethane are available on ebay for about $60. The whole thing with pump is available for about $200.

https://www.ebay.co.uk/itm/125457695169 ... BMoqzuz7hi

Very likely there's a cheaper way of doing it by picking things up second hand or improvising.

Then there's the potting compound. The only mention in the article was of a two compound resin, which could be one of hundreds of products. He didn't mention baking to get rid of moisture. It wasn't even clear it was for potting. It could be that any old urethane casting resin (as found on ebay) would do.

Henkel sell a range of electronic potting products. There's even a guide to choose the right one and at the end you can request a sample. It doesn't make it completely clear which would be best for an EHT transformer. They may be worth contacting and if their sales people are at all clued up, they can say exactly what you need.

https://www.henkel-adhesives.com/uk/en/ ... ounds.html


Not much if you are going to be doing a transformer every other week or a higher volume. Quite a lot of trouble and expense for a one off and then maybe another one in a couple of year's time. Then it's more clutter to keep somewhere.

[Cubdriver]

If memory serves, the earlier HV transformers Tek made were potted in beeswax, and the troublesome ones reared their ugly heads after they started using epoxy in those put in the 547s. My inclination would be to try beeswax after either rewinding or thoroughly drying an epoxy potted one. Haven’t thoroughly thought the process through yet, though figuring out how to get the winding degassed and impregnated with molten wax inside the vacuum chamber will be the challenge. Perhaps immerse it in molten wax then pump the whole thing down? It’ll take some experimentation.

-Pat

[MED6753]

Finally got around to pulling scope 1 apart to determine why the HV transformer failed again. It appears that I did not originally establish a tight enough seal of the enclosure resulting in moisture ingress. I have a plan to address that. In the meantime I discarded the original desiccant bags and I pulled the HV assembly. The assembly is currently back in an oven for 6 hours at approx 66 C. Also baking some new desiccant bags. I'm still going to run on the theory for now that if you keep the moisture out the HV transformer will be happy.




One change that I did not originally implement was a TekWiki recommendation to change R803 from 56K/2W to 82K/2W when the 5642 vacuum tube rectifiers are changed out for silicon rectifiers. I made that change on this scope. We'll see what affect it has on the Oscillator stabilization.

[MED6753]

More work and testing of scope 1.

Lined the HV enclosure with electrical tape to act as a gasket around the sealing surface.



HV assembly installed. Copious amounts of silicone sealant to get the best air tight seal. Is it 100%? Perhaps not but much better than previous attempts.



I discovered that R836 (1M, .25W) had increased in value to 2.3M. Replaced it with a modern carbon comp but I was concerned it would arc over. But so far there's been no issues.



First power up. Nice trace. V800 grid voltage 45.7V and HV Test Point -1845V vs spec of -1850V. Everything looks good.




After 1 hour the grid voltage increased to 54V which is great. This is the point where it went into voltage runaway last time.



After 2 hours. Still looking good but has not stabilized. Voltage still increasing slightly.



I only had time today to conduct the test for 2.5 hours. The grid voltage had increased to 65V and was still increasing slightly. No stable point as of yet. But it hadn't gone into voltage runaway either. So results so far are inconclusive. The stable point could be much higher. For example, Scope 2 goes to 85V then backs off to a stable point. The same might be true here. I'll have to conduct another test.

[BU508A]

Med, do you know this video?

[MED6753]

Yes, I am aware of that video and I've seen it before. He's located in Oz. And a member of the Facebook Old Tek Scopes group. And guess what? He won't rewind transformers for others. I shall be nice and say nothing.

[Cubdriver]

Funny, I was looking at that video the other night. Just bought a non-working 556 from a guy on the Tek mailing list and was searching on it and found that. It already had a like from me, so I probably watched it last year when we were previously talking 547 HV transformers. Brown Santa currently has the 556 in his sleigh; fingers crossed it arrives unscathed.

-Pat

[BU508A]

Yes, I am aware of that video and I've seen it before. He's located in Oz. And a member of the Facebook Old Tek Scopes group. And guess what? He won't rewind transformers for others. I shall be nice and say nothing.

What do you think about this paper?

https://w140.com/tekwiki/images/8/83/HV ... Rev_02.pdf

[Cubdriver]

Yes, I am aware of that video and I've seen it before. He's located in Oz. And a member of the Facebook Old Tek Scopes group. And guess what? He won't rewind transformers for others. I shall be nice and say nothing.

What do you think about this paper?

https://w140.com/tekwiki/images/8/83/HV ... Rev_02.pdf

At a cursory glance, I think that will be very useful! Thanks for the link!

-Pat

[Zenith]

That's the same paper I referenced above by Marco Morelli. The big shortcoming was that apart from mentioning a "two component resin" he didn't mention how they were potted.

The video is interesting, but it's a bit of a task to make up a winding machine like that, with parts available. I suppose the job could be done by hand. There are a couple of follow up videos. In one he shows potting the rewound transformer in beeswax, which you mentioned as a potting compound earlier. It isn't a very sophisticated set up. He has a jar of beeswax in a saucepan of hot water (beeswax melts at 62 to 63C), which he puts the transformer in. There is a vacuum sealed lid with a connector for a vacuum pump. I'd guess the vacuum pump was something cheap and easily available. It's not as if you need a near perfect vacuum as in a CRT.

https://www.youtube.com/watch?v=HEKOcMGyJMw

Beeswax sells for £9 for 1kg on ebay. Cheaper than synthetic resins. Even given that the transformer has to be immersed, 1kg should go a long way.

[bd139]

Looks like a faff. Sell the tubes on eBay, take the rest to the tip and retire

(only joking)

Actually watching this thread with interest for reference

[Cubdriver]

That's the same paper I referenced above by Marco Morelli. The big shortcoming was that apart from mentioning a "two component resin" he didn't mention how they were potted.

The video is interesting, but it's a bit of a task to make up a winding machine like that, with parts available. I suppose the job could be done by hand. There are a couple of follow up videos. In one he shows potting the rewound transformer in beeswax, which you mentioned as a potting compound earlier. It isn't a very sophisticated set up. He has a jar of beeswax in a saucepan of hot water (beeswax melts at 62 to 63C), which he puts the transformer in. There is a vacuum sealed lid with a connector for a vacuum pump. I'd guess the vacuum pump was something cheap and easily available. It's not as if you need a near perfect vacuum as in a CRT.

https://www.youtube.com/watch?v=HEKOcMGyJMw

Beeswax sells for £9 for 1kg on ebay. Cheaper than synthetic resins. Even given that the transformer has to be immersed, 1kg should go a long way.

I just recently watched the one where he potted the winding assembly in beeswax - very clever how he did it - I'd been mulling over how to keep the beeswax molten in the vacuum chamber and never thought of doing it on a much smaller scale using a jar in hot water with an exhaust tube to pump it down. Great idea. Now I need to figure out where the coil winding jig fabrication instructions I bought a few years ago have disappeared to...

-Pat

[MED6753]

I could never wind a transformer myself due to dexterity issues. I was born with Essential Tremors (Google it) that affects my hands (always) and sometimes my legs. It makes fine detail work difficult and sometimes near impossible. And unfortunately as you get older it tends to get worse. So that's why I work with the "big stuff" and you'll never see me doing surface mount work. I just can't do it with unsteady hands. Winding a transformer and dealing with the fine wire would result in a tangled mess. So my preference if I decide to get these HV transformers re-wound is to find someone who has experience doing it and of course compensate them. I think I'll re-join the Tek group and despite some of the grouchy bastards who don't like to share info ask if someone does provide this service.

[nixiefreqq]

I could never wind a transformer myself due to dexterity issues. I was born with Essential Tremors (Google it) that affects my hands (always) and sometimes my legs. It makes fine detail work difficult and sometimes near impossible. And unfortunately as you get older it tends to get worse. So that's why I work with the "big stuff" and you'll never see me doing surface mount work. I just can't do it with unsteady hands. Winding a transformer and dealing with the fine wire would result in a tangled mess. So my preference if I decide to get these HV transformers re-wound is to find someone who has experience doing it and of course compensate them. I think I'll re-join the Tek group and despite some of the grouchy bastards who don't like to share info ask if someone does provide this service.

let me get this straight.

the guy whose icon has been flipping us off for years just called some other gentlemen "grouchy bastards".

is there a scale for measuring grumpiness? kilogrumps? megagrumps? or would it be logarithmic like the Richter scale?

[Cubdriver]

I could never wind a transformer myself due to dexterity issues. I was born with Essential Tremors (Google it) that affects my hands (always) and sometimes my legs. It makes fine detail work difficult and sometimes near impossible. And unfortunately as you get older it tends to get worse. So that's why I work with the "big stuff" and you'll never see me doing surface mount work. I just can't do it with unsteady hands. Winding a transformer and dealing with the fine wire would result in a tangled mess. So my preference if I decide to get these HV transformers re-wound is to find someone who has experience doing it and of course compensate them. I think I'll re-join the Tek group and despite some of the grouchy bastards who don't like to share info ask if someone does provide this service.

let me get this straight.

the guy whose icon has been flipping us off for years just called some other gentlemen "grouchy bastards".

is there a scale for measuring grumpiness? kilogrumps? megagrumps? or would it be logarithmic like the Richter scale?

Would the units be in Grumps, or perhaps in MEDs?

There are Smoots marked on a bridge in Cambridge, MA...

-Pat

[BU508A]

I could never wind a transformer myself due to dexterity issues. I was born with Essential Tremors (Google it) that affects my hands (always) and sometimes my legs. It makes fine detail work difficult and sometimes near impossible. And unfortunately as you get older it tends to get worse. So that's why I work with the "big stuff" and you'll never see me doing surface mount work. I just can't do it with unsteady hands. Winding a transformer and dealing with the fine wire would result in a tangled mess. So my preference if I decide to get these HV transformers re-wound is to find someone who has experience doing it and of course compensate them. I think I'll re-join the Tek group and despite some of the grouchy bastards who don't like to share info ask if someone does provide this service.

A friend of mine has the same issues. Sorry to hear that you are also facing this challenge.

I've found the other day this forum for Fischertechnik and this introduction of a winding machine for coils.

https://forum.ftcommunity.de/viewtopic.php?t=2763

The machine in action (language is German):

Perhaps it would be possible to adapt this machine for winding transformers. Need to think more about that, because it sounds to me like a fun project. And maybe there could be some interest in the Tek community to get some HV transformers rewound.

[MED6753]

I could never wind a transformer myself due to dexterity issues. I was born with Essential Tremors (Google it) that affects my hands (always) and sometimes my legs. It makes fine detail work difficult and sometimes near impossible. And unfortunately as you get older it tends to get worse. So that's why I work with the "big stuff" and you'll never see me doing surface mount work. I just can't do it with unsteady hands. Winding a transformer and dealing with the fine wire would result in a tangled mess. So my preference if I decide to get these HV transformers re-wound is to find someone who has experience doing it and of course compensate them. I think I'll re-join the Tek group and despite some of the grouchy bastards who don't like to share info ask if someone does provide this service.

let me get this straight.

the guy whose icon has been flipping us off for years just called some other gentlemen "grouchy bastards".

is there a scale for measuring grumpiness? kilogrumps? megagrumps? or would it be logarithmic like the Richter scale?

Would the units be in Grumps, or perhaps in MEDs?

There are Smoots marked on a bridge in Cambridge, MA...

-Pat

<--------Admitted grouchy old bastard. The difference is that I freely share information to anyone who asks. The grouches on that list for some reason tend to be stingy with info and if you're not part of the "click" downright rude.

[Cubdriver]

This one looks very interesting, unfortunately he hasn't published the drawings. Something I'd eventually like to construct (in my spare time, so called because I have so little of it!)

https://technitoys.com/a-homemade-progr ... il-winder/

-Pat