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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 12th Feb 2007, 7:25 pm   #1
Giulio Maiocco
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Default LOPT rewinding

Hi,

I have a LOPT with 2 sections of the winding o/c (the tap for the linearity coil and the tap for the B+ boosted).
The biggest problem is that all the transformer is wave-wound and you have also to unwind the overwind to fix the problem. Could someone rewind it without having to pay an arm and a leg?
I could unwind it and write down the number of turns if this helps. I think finding another one is not an option, as this is for a 21" 70 TV set (all the 70 stuff is quite rare here in Italy, let alone a 21" from 23 August 1956)...

Thanks

Giulio Maiocco
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Old 12th Feb 2007, 7:41 pm   #2
Steve_P
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Default Re: LOPT rewinding

Two people spring to mind...

Murphymad (Mike Barker) on here is the head of the BVWS and he does things like this.
Ed Dinning also does them as well.

Hope this Helps.

Cheers,

Steve P
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Old 12th Feb 2007, 8:55 pm   #3
Ed_Dinning
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Default Re: LOPT rewinding

Hi Gents, I try to avoid EHT overwinds as it is impossible to get the wire to allow wave winding. If it is possible to remove the overwind intact, or fit one from another set, it should be an easy job to re-wind the various other windings. Use modern double insulated wire and polyester transformer tape.
Impreg in candle wax afterwards.

Ed
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Old 12th Feb 2007, 9:33 pm   #4
Giulio Maiocco
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Default Re: LOPT rewinding

Hi,

The problem is that also the primary is wave-wound, so I don't want to take the chance to rewind it in a "more conventional" fashion only to discover that it doesn't work, it is a very difficult job to extract the chassis from the TV, it took me 1/2 hour and you have do desolder quite a bit of wires from the yoke and the 3 loudspeakers!

Also, I think it is quite difficult to extract the overwind, it is kept in place with some sort of cloth scotch impregnated in glue, so it is very likely I damage the overwind if I try to remove it...

Cheers

Giulio Maiocco
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Old 17th Feb 2007, 5:16 pm   #5
Giulio Maiocco
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Default Re: LOPT rewinding

Hello,

These are 2 photos of my first attempt to rewind a LOPT

Just let me know if my work is acceptable

Giulio Maiocco
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Old 17th Feb 2007, 6:03 pm   #6
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Default Re: LOPT rewinding

Quote:
Originally Posted by Giulio Maiocco View Post
Hello,

These are 2 photos of my first attempt to rewind a LOPT

Just let me know if my work is acceptable

Giulio Maiocco
Good evening,
For me the pics are too much defocused.
How much KVs do you expect?

Kind regards,
Darius
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Old 17th Feb 2007, 6:37 pm   #7
Giulio Maiocco
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Default Re: LOPT rewinding

Hello Darius,

The CRT (21FP4C) needs about 16KV on the second anode, is there a method to test it without having to re-mont it in the set, it is quite difficult to extract the chassis from the TV set, it requires at least 1/2 hour and you have to desolder the wires from the deflection yoke. I was thinking to build a small circuit with an ECC82 as line oscillator, a 6BQ6 line output tube, a 6AX4 damper and a 70 yoke, to test the rewound LOPT. What is the worst thing that could happen if the transformer is not OK?

Thanks

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Old 17th Feb 2007, 6:58 pm   #8
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Default Re: LOPT rewinding

Good evening,
I have no experience with this kind of LOPT.
Maybe you get arcing to the ferrite core on the opposite side?
But it seems you have enough space there.
I think you definitely have to test it in the set.
Good luck,
Darius
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Old 17th Feb 2007, 7:02 pm   #9
Giulio Maiocco
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Default Re: LOPT rewinding

Hello,

these are better photos of my rewinding work

I keep my fingers crossed that this transformer works!!

Kind Regards

Giulio Maiocco
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Old 17th Feb 2007, 7:35 pm   #10
Ed_Dinning
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Default Re: LOPT rewinding

Hi Giulio, that looks like a good job, but the only way to test it is in the set, unless you can replicate the circuit exactly on the bench.
Before powering up make sure all capacitors across the transformer are good. An open circuit cap is possibly worse than a short circuit one as it will allow high peak voltages.

Ed
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