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#2
07-07-2015, 08:28 AM
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look for a cap that goes from the vert out tube plate to the plate of the video out tube. there is a RC circuit in there that prob is used to aid in vertical blanking. See if its one of those paper cap in ceramic tube types. IIRC zenith used a couple of those 1kv ceramic tube caps, that may be one of them.
I cant say for sure if it would improve the vert blanking but again its the kind you cant really test a rated voltage, and it prob takes a beating from the vert spike. I think most of the time its more CRT related than circuit related, I even looked into better vert blanking patents posted to improve blanking by sending a pulse to the screens of the CRT. If there were patents for it and circuits designed for it I presume it may have been an issue back in the day, at least for early color sets. On my sets with really good CRT's its never an issue. here is me looking into vert blanking issue (RCA not a Zenith though) https://www.youtube.com/watch?v=39DlVjo9hSY 
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#3
07-07-2015, 08:35 AM
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Quote:
dual function. Probably a 6GH8 or 6KT8 If you have a Sams look along under the video amp tubes thats where they usually put it. It may use diodes instead. What it does is turn off the video during retrace. If its not turned off you get lines & often strange symptoms. Whatever you are using may also be adding to the problem. DVD's VCR's, Digital CATV were not designed for the old sets. By the mid 70's almost all roundies were gone in our area. https://en.wikipedia.org/wiki/Horizo...nking_interval There is more to know than in audio but its a good start, more than most have ! 73 Zeno
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