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Old 25th Jan 2018, 12:14 am   #33
1100 man
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Join Date: Apr 2016
Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK.
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Default Re: Dismantling LOPT's

Hi John,
Many thanks, as always, for sharing your experiences of LOPT rewinding! I had a go at one when I was a lad. Dad had brought home a Decca Brunswick 22" delta tubed colour set given to him by a work colleague. We could never get the line stage to work and condemned the LOPT.
I unwound it, layer by layer, counting the turns and making notes. AFAIR, I did manage to rewind it, but the bobbins were a bit fat!
The set still didn't work so I'll never know if my transformer was functional or not!

Anyway, back to the transformer in my original post. The wax has now been removed and the EHT winding (I hesitate to use the term 'overwind', as it's a separate bobbin on the other limb of the core, rather than wound on top of the primary) can now be examined under a lens.
The problem was arcing somewhere near the entry to the winding and a small plume of smoke.
The plastic former was easily removed from the winding and as can be seen in the picture, a black carbonised mark was evident. The former has a crack running through it and a carbonised mark on the inside. The inside of the winding, which seems to be an SRBP type material, also has a carbonised mark.
It would seem that the input to the winding has been arcing through its SRBP former, then through the plastic former to the ferrite core of the transformer.
So hopefully, with some careful cleaning and re- insulation, the winding can be saved.
I must say I will be well chuffed if I can repair it as I had condemned this transformer as needing re-winding a couple of years ago.
Compare how the winding looks now to how it did in pictures 1 &2 in the first post of this thread when it was covered in black wax. It's now half the size with no wax coating!
All the best
Nick
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