Revox A77 - ELECTRICAL ADJUSTMENTS AND MEASUREMENTS; 6.2. Tape Speed

4. Changing the supply frequency from 50 to 60 Hz varies
motor speed by less than . 05 %.
Point 4 shows that the supply can be alternated between
50 and 60 Hz with absolutely no changes in circuitry.
The new motor is considerably lighter than synchronous
motors were to date. It has neither flywheel mass nor a
soft clutch. The capstan axis is rigidly fixed to the rotor,
making interchanges very easy. The relatively low speeds
of the capstan motor ( 400 and 800 rpm ) provide a large
diameter capstan axis.
Notes
25