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Technology and Culture 42.4 (2001) 737-749



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Research Note

Experts at Play
Magnetron Research at Westinghouse, 1930-1934

Karl Stephan

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"The most valuable cargo ever brought to our shores" is how one American historian, writing shortly after World War II, described the cavity magnetron tube that constituted the heart of most Allied radars. 1 Developed by British researchers in 1940 and delivered in secrecy to the United States for mass production, the legendary tube produced powerful, pencil-thin pulses of microwave beams that lit the way to victory for thousands of Allied bombers and ships. Yet the British cavity magnetron was only the latest in a series of magnetrons developed under far different conditions than the intense pressures of wartime research. At the 1933 Century of Progress Exposition in Chicago, Westinghouse Electric and Manufacturing Corporation demonstrated a complete microwave communications system that used a magnetron tube developed by a young researcher named Ross Kilgore. In the absence of wartime needs or market pressures, Kilgore's work took place in the context of a gentlemanly competition among radio engineers. Power and frequency records served as a means of keeping score in the game, and anyone who broke one of these records with a new vacuum tube held the prize until the next record-breaking device came along. In a little over five years at Westinghouse, Kilgore played the game well enough to achieve a measure of renown in his profession. His technical triumphs did not translate immediately into commercial success for Westinghouse. Indeed, the company laid him off in the depths of the Great [End Page 737] Depression. But, almost by chance, Kilgore's magnetron tube proved crucial for a pioneering experiment in quantum physics that opened the field of microwave spectroscopy and paved the way for the maser and the laser.

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The radio business in the 1920s developed along two separate lines: point-to-point services and radio broadcasting. Before vacuum tubes became widely available after World War I, point-to-point radio communication, which carried ship-to-shore and intercontinental traffic, was carried out at very low frequencies, typically below 100 kilohertz; high-power spark and arc transmitters and the passive detectors of the day did not work well above that range. But once experimenters began to use vacuum tubes to build efficient transmitters and sensitive receivers that worked at frequencies from 3 megahertz up to as high as 30 megahertz, amateur and professional radio operators found that the so-called shortwaves propagated easily around the world at certain times of the day and certain seasons of the year. This discovery caused a boom in shortwave communications, which put pressure on radio engineers to develop tubes that operated with better efficiency at higher and higher frequencies.

In the meantime, the explosive growth in domestic radio broadcasting in the United States during the mid-1920s created a huge demand for broadcast receivers, and a smaller but proportionately increasing demand for broadcast transmitting equipment. Westinghouse, as a member of the radio patent pool that included General Electric, American Telephone and Telegraph (AT&T), and the Radio Corporation of America (RCA), took advantage of basic vacuum-tube patents to develop high-power transmitting tubes for the medium-wave broadcast frequency range of 500-1500 kilohertz. By the late 1920s, the firm sold a line of water-cooled tubes that produced 20 kilowatts or more of radio-frequency energy. Even the most efficient high-power tubes still dissipated thousands of watts of energy as waste heat, which had to be removed from the copper anode and other glass and metal parts of the tubes by rapidly flowing water to keep them from melting. 2 High-power vacuum tube designers poised their creations nicely near the edge of failure, not so close that the tube's lifetime was diminished to an uneconomical brevity, but not so far away that it delivered less than the advertised amount of power.

Westinghouse's leading engineer in this new field was a Russian émigré named Ilia Emmanuel Mouromtseff. He and fellow Russian army signal [End...

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