That "thingy" also appeared on many record turntables as well.

Simple mechanical change of pulley, drivewheel or gear diameter to allow for speed change, this because the marvelous invention of Nikola Tesla, the rotating field brushless AC motor, is locked to the frequency of the AC line. Changing the speed of the motor itself would have required quite a lot in the way of circuitry and parts, while simply changing the ratio of the drive, much like as done with a two speed bicycle or automobile transmission, resulted in a solid design that does not break the bank in costs.


During the heyday of analog electronics, he Mech E. could often step in and teach the EE a trick or two, and it was also often the case where either crossed fields with virtual impunity as well.

--Mac

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