Dueling Heathkits

[kf4rca]

One of the problems with those modular sets is intermittent connections. When you put the set in its final position, you need to re-seat all the modules.
At one time, all manufacturers made modular sets. But it was soon discovered that all the connections created intermittent problems. So they returned to a unitized chassis design.
To create a video input, you'll need to go in at the emitter of Q312 with 3.5 Volts P-P on non-inverted video.