In 1930 the Ampico model B tempo levers did get quite warm.  This fact
was printed in the instruction sheet with the new Ampico.

The reason the tempo lever gets warm is because there is a resistance
coil located in the box containing the control.  This coil burns some
of the electricity in exchange for slowing down the electric roll
drive.  It is very similar to an old style electric mixer -- they got
warm too!

Modern technology, would use a device which sends varied pulses of
electricity to the motor, and would not produce heat thus saving a bit
of electric power.  Back in 1930, the only device to slow a motor down,
was one that "borrowed" some of the electricity, and burned it harm-
lessly, before it reached the little motor.  There was no saving of
electric power, as it used the same amount as if turned on full speed.
Modern speed controls are more efficient.

The warmth created by this device, could be thought of as beneficial:
it drives out moisture in humid conditions !

Bruce Clark