RCA Victor 21-T-8205 issues

[Electronic M]

By waviness do you mean to say that with a digital source after a while the top of the screen starts to flag wave in a similar manner to what it does with a VCR?

If so there are a few things I would do: Change the lytics in the power supply (so we know the B+ rails will be stable) if you have not already done so. Make sure all caps in the AGC, sync separator, Horizontal AFC, Horizontal oscillator, and H output have been changed, and make sure all resistors in those stages are within tolerance, also confirm the tubes in those stages are healthy.

After doing that it may be wise to adjust the AGC after it has warmed up long enough for the sync to have gotten wavy. If the AGC is too high or too low sync may be affected. The AGC pot will have a low no signal zone where the picture fades to white, a good zone where sync is strong, and an overload zone where the pic will go negative and loose sync, and the audio may turn to buzz. Generally you turn up till you hit the overload region then back down just past the point where overload symptoms stop (some service lit for some sets specifies 1/4 turn below overload).