Back to the VT-71H

[bandersen]

Between the detector and the CRT.
Check the signal at the grid of the video amp.
Check the signal at the plate of the video amp.
Check the signal at the cathode of the CRT.

Note that the sound is picked off the screen of the 6AU6 video amp while the video comes off the plate. So I'm thinking it's possible that circuit is screwed up in some way that allows the signal off the screen to be OK, but not from the plate.