I developed this modified composite video output circuit for my Tandy Color Computer 1. It seems to produce good stable video. The connections to U12 (or U6) are relics from the original schematic that this was based on. Now the only connections to U12 (U6) are for +5V power and ground. In the original schematic there was another connection to U12 (U6) on pin 12 to get a video signal, but I found that getting the signal from that pin caused several issues, one was that the colors on a PMODE 4 graphics screen came out wrong, another was that it interfered with and distorted the original RF output. So I moved the point where the circuit gets it video signal from to PIN 1 of the RF modulator instead, which only left the +5V and ground connections attached to U12 (U6). You could really use any convenient source of +5V and ground, it does not have to be the pins I used on U12 (U6).