The control circuitry for an alternator transmitter takes into account that the drive motor needs to receive more power during key down than during key up condition.  The key not only drives the magnetic amplifier that passes or shuts off RF, but also an auxiliary circuit that throttles back power to the motor when the key is up.  There is a grand rheostat to trim the key-up speed to match the key-down speed.  However, I expect this is a fairly delicate balancing act; and, I don't believe the motor control system can respond quite as quickly to a state change as the magnetic amplifier does.

 

John