Re: video tx
This TV transmitter circuit should work fine, I remember I’ve built something similar years ago.
The DC voltage on base of Q4 should be zero, because this works in Class C and the transistor is DC biased by the incoming RF signal.
Check if Q3 is oscillating, looking for signal in UHF TV band. The DC supply in the collector of Q4 is AM modulated by the video signal (Q1, Q2).
R4 (15k) needs some adjustments to get the right black level.
There is a need of a decoupling cap (100pF) on the emitter of Q2, that I don’t see on your schemataic.