page_title: Henry Harrison Chase Dunwoody
section_title: After DeForest
hierarchical_section_title: Henry Harrison Chase Dunwoody / After DeForest
caption_attribution_description: English: A carborundum crystal detector, an early semiconductor diode, used as a radio detector in 1920s radios. Invented in 1906 by Henry Harrison Chase Dunwoody, It consists of a piece of carborundum (silicon carbide) attached to one terminal, with a spring-loaded pin making contact with the surface. Since the carborundum detector didn't require the delicate "cat's whisker" contact needed by other cat's whisker detector crystals such as galena, it didn't have to be adjusted before each use and could be made in the form of a sealed cartridge. In addition to crystal radios, this type was also used in some powered vacuum tube radios because it was more sensitive to weak stations than the grid-leak vacuum tube detectors usually used. In use it was usually biased by a DC voltage of 3-4 volts to operate at the most sensitive point of its current-voltage curve.
context_page_description: Known in his own time for his work with the Army's Weather Bureau, Henry Harrison Chase Dunwoody invented the carborundum radio detector in 1906. It was the first practical mineral radio wave detector and the first commercial semiconductor device.
context_section_description: Dunwoody stayed with the company, now reorganized as the United Wireless Telegraph Company, for a brief time. In 1912 United Wireless, weakened by scandal and patent disputes, was absorbed by the American Marconi Company. Properly configured, carborundum makes a very sensitive detector, and by now had become a favorite of wireless operators. Marconi used it in the first successful commercial station to signal across the Atlantic, between Louisbourg, Nova Scotia and Letterfrack, Ireland in 1912. It was replaced only gradually by the simpler galena and cat whisker detector of Greenleaf Whittier Pickard, and made a resurgence in the 1920s thanks to the efforts of Acheson's Carborundum Company.
  Dunwoody remained active in research, patenting electronic devices as well as armaments. By 1911 he was president of the Aztec Copper Company, managing small claims near Organ, New Mexico. He died January 1, 1933 in Interlaken, New York.
caption: A fixed carborundum detector produced by the Carborundum Company, 1925.
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