DC restoration (can o' worms opened)

[David Roper]

The Emerson 610 is one of my favorite electrostatic sets. There are a couple of videos uploaded to YouTube showing operating sets. One shows what looks like very typical performance of an entry-level set, but the other video is extraordinary not only for image sharpness, but what is apparently a constant black level with genuine fades to black. Intrigued by the difference, I took a look at the schematic to see which one was performing as designed.

I posted a message on the linked video asking the uploader if he had added a diode when he restored his set. This was his surprising response:

I must admit I didn't spend too much time so far with that tv.
Unlike most other sets from that period its video signal is fed to grid 1 of the crt and not to the cathod, at grid 1 the video signal is mixed with a low dc from the high voltage oscillator so a stable dc is
present
at grid 1. But thinking of it, you are right! The basic black level of the picture is not recreated through this measure as the dc level is always the same.

Where should I place that diode you propose? From grid 1 to ground as seen in other tvs? But there the video signal goes to the cathod...

I saw the connection of G1 to the HV oscillator in the schematic but didn't think it had anything to do with DC restoring. Does it? Can the difference between the above linked demonstration and this one be chalked up to nothing more than misadjusted brightness?

I leave it to the experts.