... I do not own any of the original german studio / broadcast cassettes of the late tube technology phase like V72 etc. with the Tuchel connectors. But it seems to me, that most of the schematics have zero Volt lines not connected to the earth/case ground. Maybe I'm wrong, I've never seen the racks either, but if not, what was the reason for this seemingly strict separation of Zero and case/earth ?
edited: case not chassis - chassis might have been on 0V.
In a multi amplifier environment such as a desk, the zero volt lines from the V72's were taken back to a bus, and this bus made one connection to the desk chassis and earth at the rear of the desk.
At the amplifiers, although the metalwork of each amplifier would be in contact with the rack and frame metalwork once inserted into the rack, it was also usual to bond the chassis connection on the amplifier's tuchel connector to the rack chassis.
The only other connection to the individual amplifier's chassis were cable screens, both inside the amplifier, and on the cable forms running to/from the rear connector. Only one end of the cable screens on the cabling was connected to a chassis point.