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Old 24th Feb 2021, 3:30 pm   #174
Helder Crespo
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Join Date: Sep 2019
Location: Crystal Palace, Bromley, London, UK.
Posts: 417
Default Re: My first telly TV22

Quote:
Originally Posted by Travellingwave View Post
Hi Helder

No I didn't I was a bit worried that if I covered the whole thing in varnish inside the primary that it would not neccesarily get to where it needed to go and would make a hell of a job to dismantle if a fault subsequently occured. SO I just coated the overwind.

I have just checked and I have have about 50 ohms between the primary and secondary of the transformer with it still in circuit - I have read that they often fail with secondary to primary shorts - if I measure in circuit I presume there should be no resistance here?

Looks like lopt is going to have to come out
Yes, to my knowledge the primary-secondary shorts are the main cause of failure. The turps + varnish process was described on the forum by Argus25, whose lopt has behaved flawlessly since he varnished it (overwind + primary/sec) many years ago. So it's a one-off restoration, but it should really last. Leaving the primary/secondary without any protection is risky, and there are many more stories of people with shorted primaries (me included) than with problems in varnished lopts (none that I know of). The pattern is the same as in the lopt of my first tv22. it worked well for a few hours before kicking the bucket. So you'll have to get it rewound. You'll probably have to change the 470pF cap after that to get the same / similar behavior (EHT, width, etc.)
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