Amplidyne

An amplidyne is an obsolete electromechanical amplifier invented prior to World War II by Ernst Alexanderson.

Historically, amplidynes were one of the first amplifiers to generate very high power (tens of kilowatts), allowing precise feedback control of heavy machinery.

Vacuum tubes of reasonable size were unable to deliver enough power to control large motors, but vacuum tube circuits driving the input of an amplidyne could be used to boost small signals up to the power needed to drive large motors.

The system (diagram right) is a feedback control system in which a feedback signal from a sensor representing the current position of the gun is compared with the control signal which represents the desired position, and the difference is amplified by the amplidyne generator to turn the gun mount motor.

A phase-sensitive demodulator, with the synchro AC power as its reference, created the DC error signal of the required polarity.

[citation needed] Used to remotely operate the control rods in early nuclear submarine designs (S3G Triton).

Three amplidynes, from a 1951 General Electric advertisement (not to same scale). (top left) 1 kW amplidyne motor-generator, (bottom left) 3 kW amplidyne motor-generator, (right) 5 kW amplidyne generator.
Figure 1 of the patent drawing
Amplidyne circuit as used in U.S. Navy naval gun control. This is a high-power position servo system.