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Magnetic amplifier
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===Early development=== A voltage source and a series connected [[variable resistor]] may be regarded as a [[direct current]] signal source for a low resistance load such as the control coil of a saturable reactor which amplifies the signal. Thus, in principle, a saturable reactor is already an [[amplifier]], although before 20th century they were used for simple tasks, such as controlling lighting and electrical machinery as early as 1885.<ref>{{cite book |author=Electronics Design and Development Division |title=Magnetic Amplifiers β A Rising Star in Naval Electronics |date=May 1954 |orig-year=1951 |publisher=Bureau of Ships, Department of the Navy |location=Washington, D.C. |id=NAVSHIPS 900,172 |page=2 |chapter=History |quote=The magnetic amplifier is not new β the principles of the saturable core control were used in electrical machinery as early as 1885 although they were not identified as such. |ref=Navy}}</ref><ref>{{cite book |last=Mali |first=Paul |author-link=Paul Mali |title=Magnetic Amplifiers β Principles and Applications |chapter-url=http://www.pmillett.com/Books/mag_amp.pdf |access-date=2010-09-19 |date=August 1960 |publisher=John F. Rider Publisher |location=New York |id=Library of Congress Catalog Number 60-12440 |page=1 |chapter=Introduction |archive-url=https://web.archive.org/web/20061114175548/http://www.pmillett.com/Books/mag_amp.pdf |archive-date=2006-11-14 |quote=Magnetic amplifiers were developed as early as 1885 in the United States. At that time they were known as ''saturable reactors'' and were used primarily in electrical machinery and in theater lighting. |ref=Mali}}</ref><ref>{{cite book |title=Fundamentals of Magnetic Amplifiers |last=Kemp |first=Barron |date=August 1962 |publisher=H. W. Sams |lccn=62-19650 |page=7 |chapter=Magnetic Amplifiers |quote=The use of magnetic forces for amplification is not new; a survey of its history shows that although the device was not known as a magnetic amplifier at the time, it was used in electrical machinery as early as 1885. |ref=Kemp}}</ref> In 1904 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.<ref>{{cite web |title=Ernst F. Alexanderson, The accomplishments and life of E. F. Alexanderson, 1878β1975 |date=2014 |publisher=Edison Tech Center |url=http://www.edisontechcenter.org/alexanderson.html }}</ref><ref>Milestones:Alexanderson Radio Alternator, 1904</ref> 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.<ref name=Wilson>{{cite book|last=Wilson|first=Thomas G.|chapter=The Evolution of Power Electronics|title= Fourteenth Annual Applied Power Electronics Conference and Exposition, 1999. APEC '99|year=1999|volume=1|pages=3β9|doi=10.1109/APEC.1999.749482|isbn=978-0-7803-5160-8|s2cid=117592132 }}</ref><ref>{{harvnb|Trinkaus|2006}}</ref> The experimental telegraphy and telephony demonstrations made during 1917 attracted the attention of the US Government, especially in light of partial failures in the [[Transatlantic telegraph cable|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.
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