A magnetic amplifier, or mag amp, is a type of electronic converter. The mag amp uses the interaction of electric currents, called electromagnetism, to enhance electrical signals without requiring any moving parts. This variety of power amplifier was a popular replacement for vacuum tubes, and is noted for its high reliability in harsh conditions. Basic magnetic amplifiers were built as early as the 1800s, but it was not until the 20th century that these devices saw widespread use.
Both the United States and Germany developed dependable mag amps for military purposes during World War Two. During the 1940s and 1950s, magnetic amplifiers replaced many vacuum tube amps, which performed the same general function but were more fragile. While modern transistors are now the primary method of power amplification, magnetic amps are still used in devices that must be resistant to severe conditions.
A magnetic amplifier produces a significant radio frequency (RF) signal when it is activated. This feature can be used for sending rudimentary radio messages. By toggling the amp on and off, the RF signal can be manipulated and received from a distance. For this reason, early radio pioneers experimented with using large magnetic amplifiers to transmit Morse code messages across oceans.
Magnetic amps use two duplicate coils of wire, which are each wrapped around a magnetic core. To operate the amplifier, one of the coils is energized with alternating current (AC) electricity. The circuit that is receiving amplification, called the “load,” is connected to the second coil. An electromagnetic field is generated when the first coil is powered, which also induces a charge in the load.
This setup allows the electrical load to be controlled without needing an actual physical connection or mechanical switch. Magnetic amplifiers typically have a long usable life, since there are no moving parts to wear out. For the same reason, mag amps are fairly immune to vibration or shock, and can be used in rough environments. Equipment such as arc welders and industrial power supplies sometimes use a magnetic amplifier due to these advantages.
A magnetic amplifier does have some disadvantages, however. Size is one problem. Modern transistors can perform the same function as mag amps while taking up significantly less room. Magnetic amps are also not as efficient as modern solid-state transistors, which are able to control circuits with very little power loss. The amplification ability or gain of a mag amp is relatively low compared to newer solid-state amplifiers.