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Old 24th Feb 2021, 6:49 pm   #181
Lloyd 1985
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Default Re: My first telly TV22

This is exactly how one of mine failed. I had noticed on that one that the enamel on the windings had begun flaking, probably because of damp, I did try to cover it with varnish, but it obviously didn't help in the end. I do wonder what effect white spirit will have on the old enamel insulation? Strangely, of my 2 sets, the one with the untouched LOPT is still working well, still covered in cracked up old pitch! I'm not going to touch that one.

Hope you get your set working!

Lloyd.
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Old 24th Feb 2021, 7:12 pm   #182
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Default Re: My first telly TV22

Hi Travellingwave,

It should be 36swg I think (0.2mm). When you measure the original wire you need to account for the enamel.
You may find that double insulated wire is too thick.

I rewound one using standard enamelled wire, but with transformer tape between each layer. Then there were several layers of tape between primary and secondary.

Cheers
Andy

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Old 24th Feb 2021, 8:10 pm   #183
Travellingwave
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Default Re: My first telly TV22

Thanks Andy , I measured the diameter of the wire with a digital micrometer and got 0.25 mm. So if I order new 0.25mm wire is that the outside diameter including the insulation or the diameter of the copper core?

I measured the thickness of the laminated core at each end of the coil and one end has expanded by 2 mm due to corrosion which can’t have helped matters.
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Old 24th Feb 2021, 8:31 pm   #184
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Default Re: My first telly TV22

I’ve ordered some 0.2 mm wire as well. Checking specs on IEC60317 wire , 0.25 mm grade 2 has an overall diameter of 0.29mm so is thicker than the stuff on the transformer, 0.2 mm has overall diameter of 0.239 mm so is closer I think
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Old 24th Feb 2021, 8:33 pm   #185
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Default Re: My first telly TV22

Grade 2 wire also has a breakdown voltage of 3.5 Kv , so should be up to the job
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Old 24th Feb 2021, 10:24 pm   #186
beery
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Default Re: My first telly TV22

Hi Travellingwave,
Yes the wire diameter/gauge quoted when purchasing new wire is only the diameter of the copper and does not include the enamel.

About the expanded laminations, I'm convinced that this is the root cause of TV22 line output transformer failures. I'm sure that when you unwind it, you will find the failure where the wire was been stretched. The original cellulose enamel didn't take well to begin stretched.
I always say that part of the reason that TV22s fail in this way is because the Bakelite cabinet can hide the fact that a set may have been stored in the damp.

The other problem with rusty laminations is that it increases eddy currents and these are a more serious problem where the output transformer is also the oscillator coil. I would be tempted to remove the laminations, rub them flat, straighten them, apply rust killer, apply spray acrylic lacquer on one side of each lamination and then put them back. Remember to put them the same way round, so that the varnish is on the same side of each lamination. Also put a bit of sleaving on the mounting srew where it passes through the laminations.

I do have turns data, but will have to look it up.

Cheers
Andy
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Old 25th Feb 2021, 8:36 am   #187
Travellingwave
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Default Re: My first telly TV22

Thanks Andy , I was wondering if I should be varnishing the LAMs , I presume varnishing one side is just to stop the thickness building up. Is the thickness of transformer tape between layers likely to be an issue for capacitance? With class 2 wire is it even needed?

I think I will video the post Mortem and rewind - if it works could be useful for others.

My other thought was that the failures might occur at either end of the bobbin , where the paper has probably disintegrated over the years. This might explain why in situ revarnishing might have worked for others , I struggle to believe that any varnish could penetrate very deep into the windings unless it was done under vacuum.
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Old 25th Feb 2021, 8:50 am   #188
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Default Re: My first telly TV22

Ive ordered one of these for £12.99 as a possible controller for a coil winding machine, I already have an arduino. A couple of stepper motors , one to rotate the bobbin and one with a lead screw to lay down the wire

https://www.amazon.co.uk/gp/aw/d/B07...?ie=UTF8&psc=1
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Old 25th Feb 2021, 9:03 am   #189
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Default Re: My first telly TV22

Quote:
Originally Posted by Travellingwave View Post
I struggle to believe that any varnish could penetrate very deep into the windings unless it was done under vacuum.
Tape recording heads were made in this way, although not with varnish.

A much better solution is to use Anti corona lacquer in either spray or liquid form, this does penetrate significantly into fine windings.
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Old 25th Feb 2021, 9:06 am   #190
mark pirate
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Default Re: My first telly TV22

Quote:
This is exactly how one of mine failed.
Same here, the set was working perfectly with an excellent picture, it then just faded away after running for 1.5 hours

I have had 3 LOPT failures over the years, all due to shorted primary windings.
I am sure it is due to the paper in the primary going conductive, as this has happened to a LOPT that had been dried out on a bench PSU for several days.

I am pretty certain that previous storage conditions can cause this issue, my first TV22 was stored in a warm bedroom for decades, and has had no issues since I restored it around 10 years ago.

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Old 25th Feb 2021, 10:23 am   #191
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Default Re: My first telly TV22

There's a lot of LOPT rewind information in a BVWS article here:
https://www.bvws.org.uk/publications...olume41number3

-not sure if I'm allowed to duplicate it here, unfortunately.
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Old 25th Feb 2021, 10:41 am   #192
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Default Re: My first telly TV22

Hi Travellingwave,

Quote:
Originally Posted by Travellingwave View Post
Thanks Andy , I was wondering if I should be varnishing the LAMs , I presume varnishing one side is just to stop the thickness building up. Is the thickness of transformer tape between layers likely to be an issue for capacitance? With class 2 wire is it even needed?
Lams are often varnished on one side and oil blacked on the other. Sometimes both sides are varnished. As this is a transformer that operates in the KHz range the lams need to be thinner, so more are required. You could double varnish if you can spray it thin enough (my rattlecan skills aren't great), but if you choose to do just one side, then it would be good to spray both sides of the last lamination. The insulation between laminations can be very thin as we are talking about micro volts between laminations. Laminations are not great in this application, but suitable ferite ceramic materials had not been available when the TV22 was designed.

Capacitance between layers using transformer tape is not an issue with this transformer. You will find that the original paper between layers is even thinner than the tape, it is like fag paper. Note that when you rewind with polyester transformer tape you don't really need to varnish it (dives for cover).It won't hurt to seal it with some anti corona laquer spray though.

I don't think that grade 2 wire is required here, iindeed it might take up too much space.

Winding details.
Refering to the attached picture:-
Rewind the transformer using 0.2mm diameter wire.
There are 60 turns between pins 1 & 2,
631 turns between pins 2 & 3,
1042 turns between pins 4 & 5 and
312 turns between pins 5 & 6.

I measured this many years ago and it might not be 100% acurate, however the rewind I did performed just fine.

Cheers
Andy
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Old 25th Feb 2021, 2:19 pm   #193
Travellingwave
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Default Re: My first telly TV22

There's a lot of LOPT rewind information in a BVWS article here:
https://www.bvws.org.uk/publications...olume41number3

-not sure if I'm allowed to duplicate it here, unfortunately.

Thanks - if I follow the link it takes me to a title/index page but cant seem to find a link to the article
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Old 25th Feb 2021, 5:23 pm   #194
Dickie
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Default Re: My first telly TV22

Being a relatively recent issue it's not yet available as "free to view". You may be able to buy a copy somewhere.
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Old 26th Feb 2021, 10:39 am   #195
Helder Crespo
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Default Re: My first telly TV22

Quote:
Originally Posted by Travellingwave View Post
My other thought was that the failures might occur at either end of the bobbin , where the paper has probably disintegrated over the years. This might explain why in situ revarnishing might have worked for others , I struggle to believe that any varnish could penetrate very deep into the windings unless it was done under vacuum.
Yes, vacuum seems the best way to do it.
All I can say is that dipping the lopt in varnish (marine spar, transformer or anti-corona) while still wet from the white spirits and leaving it overnight in the varnish (the first and most important dip) seems to do the trick, i.e., no failures in the primary and no corona discharges in the overwind, unlike my first lopt which was left untouched and died on the second day after some 3-4 hours of apparently perfect operation. If my varnished lopt ever dies, I will make sure to post it on the forum.
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Old 26th Feb 2021, 4:58 pm   #196
Helder Crespo
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Default Re: My first telly TV22

Quote:
Originally Posted by Dickie View Post
Being a relatively recent issue it's not yet available as "free to view". You may be able to buy a copy somewhere.
I tried to get this issue some time ago, and sent a couple of emails to the BVWS. I will post a request to see if someone has one for sale.
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Old 26th Feb 2021, 7:17 pm   #197
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Default Re: My first telly TV22

I know I had it.
I will have a look, but I've had two house moves since then, so it might not be stored here.

Cheers
Andy
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Old 27th Feb 2021, 11:14 am   #198
Travellingwave
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Default Re: My first telly TV22

I have gathered the bits for my LOPT rewind

1. Arduino Uno with stepper motor shield
2 stepper for winding axis
3 stepper with lead screw for traverse axis
4 0.2mm magnet wire
5 transformer tape

The rest of bits I can 3D print

There are quite a few arduino based coil winding machine projects on the web for inspiration

My first step will be to set up the existing primary coil on the stepper motor and do a controlled unwinding and use the arduino to count the turns for me , I could do by hand but donít want to lose count

I will 3D print a suitable bobbin to wind the primary onto and exactly reverse the process with new wire and a layer of tape between each layer.

Thatís the theory at least!

Will video as I go and if successful post it on youtube
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Old 27th Feb 2021, 11:40 am   #199
Travellingwave
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Default Re: My first telly TV22

I have gathered the bits for my LOPT rewind

1. Arduino Uno with stepper motor shield
2 stepper for winding axis
3 stepper with lead screw for traverse axis
4 0.2mm magnet wire
5 transformer tape

The rest of bits I can 3D print

There are quite a few arduino based coil winding machine projects on the web for inspiration

My first step will be to set up the existing primary coil on the stepper motor and do a controlled unwinding and use the arduino to count the turns for me , I could do by hand but donít want to lose count

I will 3D print a suitable bobbin to wind the primary onto and exactly reverse the process with new wire and a layer of tape between each layer.

Thatís the theory at least!

Will video as I go and if successful post it on youtube
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Old 27th Feb 2021, 12:17 pm   #200
beery
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Default Re: My first telly TV22

Hi Travellingwave,
That sounds great.
Do make note of the number of turns per layer. This has to be the same for each layer (except the final one). This ensures that subsequent layers have a flat surface to rest on. There is a paxolin coil former which the windings sit on. Reuse that, though you may have to cover it in a layer of tape first as it may have split due to the rusty laminations.
I've had coil winder bobbin adapters made (rather than bobbins) and it is certainly less labour intensive than the normal method of planing down bits of wood and drilling centre holes.

These days I wind transformers on an AVO Douglas coil winder. These are very old and when they turn up they often have parts missing. It took a lot to get mine going. I made up a control circuit using two PICs (one isolated and one on the high side), to drive a washing machine motor via a triac.

When I originally rewound the TV22 line output transformer, I did it myself, making use of a winding machine at a local transformer manufacturer (long since defunct). They only had enormous manual feed machines, which made trying to get the wire neatly side by side a real pain.
It was a very odd set up with the boss having started up on his own after being employed at another winding company. He had equipment that was too big for the kind of contracts he had and little understanding of transformer theory.
This is relevant because he sourced new laminations for my transformer. He ordered a material much thicker than the original, stating that it would make no difference (he was wrong there) and also opted to save money not having the mounting holes punched. His idea was that to simply drill through the whole lamination stack in one go, ignoring the fact that this shorted all the laminations together. These two things would not be a problem at 50Hz, but at 10kHz it was.
They guy was also struggling with a large contract winding switched mode transformers to a customers specification, he only tested them at 50Hz and the customer rejected loads of them due to excessive noise. He blamed them for running them at high frequency! It came as no surprise that they didn't stay in business for long.
Also for this reason I have loads of the "I" shaped version of the TV22 line output transformer laminations (early sets had "T" shaped ones), that aren't much use to anybody.

Your use of an Arduino for the wire feed guide could mean it also has the potential to work as a wave winder as well.

I'll stop waffling now.

Cheers
Andy

Last edited by beery; 27th Feb 2021 at 12:27 pm. Reason: Formatting
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