Quite a difference between prop sync on a Curtiss Electric and a Ham Standard. The Ham Standard utilized the regular tach generator signal from each engine to a Sync Box. The sync box had a mechanical control from the prop lever(s). You moved the prop lever and the props then slaved to it by the box sending "increase" / "decrease" signals to the electric trim head on the propellor governors. Except for the prop lever input, the sync box was all electronic, and hence was quiet. On the L-1649 they added a sensor that picked up prop phase and signaled the prop sync box. It was truly magic and I don't remember it as giving us any trouble.
With Curtiss Electrics there was a separate prop alternator on each engine that that sat where the governor would sit. A prop sync unit was in the cockpit, It had a "master motor" whose speed was controlled by the prop lever and there was a master motor tach indicator reading the selected rpm. There was a prop contactor for each engine mounted on the master motor and their speed was driven by the prop alternator on each engine.
If the contactor's rpm matched the master motor rpm all was relatively quiet. If it didn't, an electrical contacts closed and sent power to the electric motor in the prop hub causing a increase or decrease pitch change. It was quite noisy what with the master motor running, the four contactor motors running and the electrical contactors clacking away as they sought to hold rpm. In retrospect, I wonder what it sounded like on a B-36 with six props to control.
I think that was an Aldis lamp.