TW — I agree that it sounds like a manual-autotransformer motor starter. The old Allen-Bradley versions also had a bell that, during starting, sounded after rotor speed increased to normal—signaling the operator to transfer the “slot machine” handle to the running position. [In mills in the northwest. oil-immersed contacts minimized arc-induced sawdust detonation.]
Modern autotransformer magnetic starters have taps at 50, 65 and 80% of line voltage, to allow inrush-current and starting-torque matching.
[The "prop stick" muat have been a custom accessory.]
