[old_tv_nut]

OK, this shows a DC restorer before the sync separator, So you should not need one in your input circuit, at least not for sync.

I suggest the following to try to chase one problem at a time:

1) Adjust the gain of the transistor amplifier to get normal contrast.
2) Leave it there.
3) Chase the hum bars.

To make sure I'm following right, does the cathode of VT6a (pin 3) go to pin #6 of plug P7 and hence to R201?