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It is not all that hard to figure out. With a sam's one can look for a video injection point after the video detector, and before the synch take off. Then just observe the waveform amplitude and polarity there on the schematic or in the set with a scope. with that data and the google info on the composite video signal standard one can figure out the gain needed. And then all that is needed is a simple OP amp circuit that ANYONE can design for the specific gain and possibly polarity inversion required for nearly any set. The OP amp could be powered by rectified heater voltage on transformer powered sets, though if the output amplitude is large one might need to use a voltage doubler, trippler, etc to get enough rail voltage for the OP amp....Not to mention the many other power sources both set derived and tacked in that could be devised.
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