Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors. The original documentation does not specify the maximum motor current.
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in a 1990 Electronics World magazine. The circuit can be mounted today by...