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I have the original RCA manual and the Rider's.
The TV main chassis is for sure a TRK12 because it has no limiter tube.
It has no grid cap on tube 9, no connections to pins 3 and 4,
so it must be the version in Rider's that uses IF grid bias as contrast control.
There used to be connections to pins 1, 3, and 4, but no longer,
they were cut off.
Of course, I am going to use one of the radar tubes rather than a real
12AP4 so that may make a difference in the G2 CRT bias.
Steve McVoy: do you know if the 12LP4 also needs different grid bias,
or is it non-critical for test use?
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