Well in my unpacking I came across this old piece of history, a one-inch diameter  Magnesian. It was made g-d knows when. This device has only four pins, which threw me for a loop. I did not understand how it worked until I found figure 2. Normally a Synchro is a five lead device

where you have three leads for the Stator and two leads for the rotor, on which power is applied.  What they did is like a one-cheek-sneak.

They still have power across the Rotor at pins A&B. But the third leg of the Stator is now grounded.

 


figure 1

figure 2