Dynamoelectric amplifier for power control

THE USE of amplifiers has become common knowledge in radio, but on the other hand, the term amplification has seldom been applied to processes in power engineering. Strictly speaking, we may say that a radio amplifier is only a form of control because we always tap a new source of power and the function of the amplifier is to control this power so as to reproduce the changes of energy flow at a higher power level. On this ground we might say that an ordinary d-c generator is an amplifier because we control the power output by the current in the field winding. Such a terminology would, however, be rather misleading because when we say amplification, we imply something more specific than when we say control. An amplifier should give accurate reproduction both of intensity and time intervals, whereas, controlled power circuits used so far have not met these requirements. In the radio-frequency amplifier we are dealing with a time element of less than a millionth of a second. In an audio amplifier the time element is about 1/5,000 of a second. The only device we know of that will respond in such a short time is the high-vacuum electron tube. In power circuits, on the other hand, the time element is seldom less than one-tenth of a second.