radio pioneer Reginald Fessenden placed an order for a high frequency rotary mechanical alternator from the General Electric Company capable of generate AC at a frequency of 100 kHz to be used for continuous wave radio transmission over great distances. The design job was given to General Electric engineer Ernst F. Alexanderson who developed the 2 kW Alexanderson alternator. By 1916 Alexanderson added a magnetic amplifier to control the transmission of these rotary alternators for transoceanic radio communication. The experimental telegraphy and telephony demonstrations made during 1917 attracted the attention of the US Government, especially in light of partial failures in the transoceanic cable across the Atlantic Ocean. The 50 kW alternator was commandeered by the US Navy and put into service in January 1918 and was used until 1920, when a 200 kW generator-alternator set was built and installed. Usage in electric power generation Magnetic amplifiers were extensively used in electricity power generation from the early 1960s onwards. They provided the small signal amplification for generator automatic voltage regulation (AVR) from a small error signal at milliwatt (mW) level to 100 kilowatt (kW) level. This was in turn converted by a rotating machine (exciter) to 5 megawatt (MW) level, the excitation power required by a typical 500 MW Power Plant Turbine Generator Unit. They proved durable and reliable. Many are recorded in service through the mid-1990s and some are still in use at older generating stations, notably in hydroelectric plants operating in northern California. Misnomer uses In the 1970s, Robert Carver designed and produced several high quality high-powered audio amplifiers, calling them magnetic amplifiers. In fact, they were in most respects conventional audio amplifier designs with unusual power supply circuits. They were not magnetic amplifiers as defined in this article. They should not be confused with real magnetic audio amplifiers, which also exist. See also Parametron Magnetic logic Transductor References External links Electromagnetic components Electronic amplifiers Power electronics