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Old 1st Feb 2007, 3:46 pm   #5
Ghostuser
Pentode
 
Join Date: Oct 2003
Location: Alton, Hampshire, UK.
Posts: 137
Default Re: Cracked LOPT Core

Dear John,
I have three LOPTs, from either V4 or VT4. I obtained a complete VT4 and a scrap VT4 from 'BRC 3000' and now have a my original V4 and a VT4 working, apart from the picture width issue. Part of this was caused by fried linearity coils and I am having one rewound. Substitution of one of my three lin coils for another had proved that there was a linearity coil problem - adjustment of one made no visible difference to the picture, but the swap gave me more width and some control of linearity. As to LOPTs, two of the three show signs of melting of the pitch at some time. On one, the pitch has run down the side of the transformer from the primary winding. I will not disturb anything until I have covered all other possible causes of problems as rewinds are not cheap. I guess there is a possibility that primary overheating could have been caused by excess LO anode current due to line oscillator failure at some time. Several line oscillator components had been changed on that chassis in the past, but the LOPT seemed no worse than the one from the scrap chassis when I tried a swap.

I expected TV restoration to be a pleasant challenge and I am being rewarded!

Cheers and thanks again for your interest.
Nigel
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