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Focus drift with scene brightness is a universal problem with the stock CT-100 even if the transformer is good (based on the look of mine I think the modern replacement transformer John Yurkon? made was installed by the last owner). Another member (Tom Albrecht IIRC) posted a modification to replace the fixed resistor between the focus wiper and ground with 15 200V 1W Zeners in series. I modified my CT-100 and it stopped the focus drifting with screen brightness...15 ended up being too many for me as peak focus was past the end of the control. I ended up reducing it to 12 Zeners so peak was somewhat centered on the pot.
I wonder if this solid state transformer replacement will work on the Westinghouse H840CK15?... I've got one that works but has questionable older repairs (haven't looked at its transformer yet) that I would like to get to and finish up in the next year or so.
This project is a definite asset to the community.
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