“Relatively good 6 V p-p video going into 6LF8 pin 2 and then odd stuff at the plate pin 9 at much higher amplitude.”
This does makes sense, as Sams shows the input to the 2nd video amp ( pin 2 v4 ) to be 5v ptp, and shows no wave for output of the 1st, pin 9, as that point still has the bias on there, I'd expect it to be garbage if you hook up there, but the fact that pin 2 is clean, means that it must be OK by default, one could also hook to the far side of color link cap (c22) and see what you have there.
But by default, if as you say the signal at pin 2 v4 is nominal, then 1st video should be fine, and path 21 is screwy if the signal is crap down there or something
