I know this has been addressed in the past through searching previous posts but just want to make sure I'm clear on a few things.
Given the pictures shown below I am making a few assumptions:
1. shield from cable between input xlr and Mic input Tx: shield is connected to xlr pin 1 and then earthed at the input tx? (tab attached to case?)
2. shield from cable between output tx and phase switch: shield is earthed at output tx only.
3. shield from cable between phase switch and output xlr; shield is earthed at xlr pin 1
4. B- (0v) is connected to earth (e.g chassis) at one and one place only? ( which is going to be my star gound for B- 0v )
Are you trying to understand how this wiring is done in the 1073 or are you building something and trying to understand how to wire your device?
As mentioned, the 1073 was a module like an over-sized 500 series that plugs into a card-edge connector. So the various letters correspond to pins in the connector.
But if you're building your own 1073 or parts of it with a standalone enclosure and XLRs, then you might want to follow the general rules about I/O wiring which is that:
1. The shield of the input cable is connected to pint 1. Pin 1 should be connected to the chassis at the entry point over the shortest possible length of wire. The length of this pin 1 to chassis connection will influence the frequency of RF that might be radiated within the enclosure so with RF being what it is today, this is actually important and only become more important over time. There are XLR connectors that internally connect pin 1 to a spike around one of the XLR screw holes so that it stabs the chassis.
2,3. Ideally the output should be wired the same as described in case 1 above. Unfortunately because the transformer primary has DC running through it, you probably can't just move the phase switch to the other side of the OT. But I would still make the pin 1 to chassis connection at the entry point and NOT at the OT output as suggested in the schematic. I don't think this should be a problem for the transformer shield which would still be connected to the shield of the cable.
4. There are several "ground" references in a typical electrical device with a metal enclosure (note that this does not fully apply to a plastic enclosure which is not recommended for a circuit with mains and certainly not for a circuit with a lot of magnetics like the 1073):
earth ground / protective earth / PE
Path for fault current protects the operator from a shock. This earth ground wire from the mains input should (must) be connected to the chassis at the entry with a solid mechanical connection. In a DIY project this is usually a beefy bolt with toothed washers and beefy crimped ring terminals for the connected wires.
chassis ground
Path for fault currents protects the operator from a shock and shields the enclosed electronics from EMI. Again, chassis and earth ground should be connected at mains entry with a beefy mechanical connection.
0V / signal ground
The circuit ground used by amplifiers and other non-safety related grounds. This is sometimes further broken down to AGND and PGND mean analog ground and power ground (and some use DGND to mean dirty / digital ground for relays, LED drivers, microcontrollers and so on).
0V of all circuits should converge like the trunk of a tree (which is sometimes referred to using the misnomer "star ground") at the 0V of the last filter capacitor of the power supply. Like the trunk of a tree, it should be think and solid. Using the same solder joint or another directly next to it, a separate wire should run to the aforementioned chassis bolt to connect the power supply 0V to chassis ground and on to earth ground.
Although the exact arrangement of these last bits is subject to some interpretation by others here.
