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UNITED STATES EARLY RADIO HISTORY
THOMAS H. WHITE | |
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Audion and Vacuum-tube Receiver Development (1907-1916)
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Lee DeForest invented a three-element vacuum-tube detector which he called an Audion, but initially it was so crude and unreliable that it was little more than a curiosity. After a lull of a few years, more capable scientists and engineers, led by AT&T's Dr. Harold Arnold, improved vacuum-tubes into robust and powerful amplifiers, which would revolutionize radio reception. LEE DEFOREST AND THE EARLY AUDIONS In 1906 Lee DeForest was investigating the potential of radio signal detectors that were enclosed in partially evacuated glass tubes, and he called the various configurations "Audions". At the October 26, 1906 New York meeting of the American Institute of Electrical Engineers he reviewed his limited progress so far, and this presentation was republished in late 1907 in the Scientific American Supplement as The Audion: A New Receiver for Wireless Telegraphy. Shortly after the A.I.E.E. presentation he made a critical change to his three-element design, by placing a "control" electrode, which he called the "grid", between the "plate" and "filament" electrodes. This "grid Audion" was capable of slightly amplifying received signals, but at this stage could not be used for more advanced applications, such as radio transmitters. The inefficient design of the original Audion meant it was initially of little value to radio, and due to its high cost and short life it was rarely used. John L. Hogan, Jr.'s The Audion; A Third Form of the Gas Detector, from the October, 1908 Modern Electrics, concluded that "The Audion is capable of being developed into a really efficient detector, but in its present forms is quite unreliable and entirely too complex to be properly handled by the usual wireless operator." In the 1909 edition of Operator's Wireless Telegraph and Telephone Hand-book, Victor H. Laughter's review of the Audion was even more pessimistic, noting how sensitive the device was as a receiver, but concluding "it is doubtful if it will ever come into wide use, owing to the difficulty in manufacture and short life". The Audion did have a strong allure for teenage experimenters, however. Its imperfect evacuation meant that, like a neon tube, it often glowed an enchanting blue or violet when in use, with the shade varying in response to changes in signal strength. And then the filament would burn out. Years later, in the September, 1926 issue of Radio Broadcast magazine, Carl Dreher reminisced in Memoirs of a Radio Engineer about the enticing but frustrating early devices -- "Flung into deepest despair by the demise of a beloved tube, or the failure of a new one which never worked at all, the audion speculator would save up his pennies and plunge again." PRACTICAL REFINEMENT Lee DeForest did not have a very good understanding of how the "grid Audion" vacuum-tube worked, and, beginning in 1912, more capable electrical engineers began teasing out its full capabilities, finding, in particular, that the tube worked best as an electron device with with a high level of vacuum, in contrast to DeForest's insistance that it operated using ions, and required a residual level of gas. Edwin Howard Armstrong's seminal paper, Operating Features of the Audion from the December 12, 1914 Electrical World noted "the explanations advanced to account for its action do not appear to be satisfactory", then went on to gave a comprehensive review of the actual working of the grid Audion. This greater knowledge led to the development of regeneration (also called "feedback") which provided greatly increased amplification as a receiver, and also led to vacuum-tube transmitters, and Armstrong reviewed the expanded functions in Some Recent Developments in the Audion Receiver from the September, 1915 Proceedings of the Institute of Radio Engineers. Armstrong had received a U.S. patent for his discoveries at the time this paper was published, and DeForest responded by filing his own competing patent application, claiming he stumbled on the same general idea in 1912. A long series of court battles ensued, and DeForest eventually prevailed, although the engineering community was largely unconvinced by his claims. Device for Receiving Wireless Time Signals from the March 27, 1915 Electrical World magazine, announced that the DeForest Radio Telephone & Telegraph Company in New York City was now selling a vacuum-tube receiver designed to receive time signals from the navy's station, NAA, located at Arlington, Virginia. But as late as 1916 the Audion vacuum-tubes produced by the DeForest company were still plagued by quality control problems, and the company supplied usage tips, such as the March, 1916 QST magazine's Practical Pointers on the Audion by A. B. Cole, which actually revealed how little they still understood about the operation of the device. In 1915, the American Telephone & Telegraph Company purchased the U.S. commercial radio patent rights for the Audion from DeForest. However, the DeForest company retained the right to make sales for non-commercial use, although initially the procedures for purchasing Audions were restricted in an attempt to increase profits. Persons were supposed to first buy a unit which included an Audion vacuum tube -- perhaps a Type RJ9 DeForest Audion Detector "Licensed for amateur or private use only", as offered through the 1916 Manhattan Electrical Supply Company (MESCO) wireless catalog. And even after this initial, and expensive, purchase, replacement Audion tubes could only be obtained by exchanging the remnants of a burned-out Audion, as explained in the Renewal Audion Bulbs section of the catalog. Eventually this restrictive policy was relaxed somewhat, after the Elmer T. Cunningham's AudioTron Sales Company in Oakland, California began selling a cheaper bootleg vacuum tube, and the DeForest company responded with the Type "T" Tubular Audion Tube, recently added to the MESCO catalog, for experimenters "who do not wish to buy complete Audion Detectors with the necessary accessories, and for those whose limited means will not permit the complete instruments to be purchased". |
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"Michael I. Pupin: I have had some experience in the constructing of detectors of electrical waves. If there must be a new name for each new detector, pretty soon the science of electrotechnics will be a maze of new names. For that reason I am opposed to new names. Although Dr. De Forest is very enthusiastic about the elegance of the name audion, I must say I am not much impressed by it. It is a mongrel. It is a Latin word with a Greek ending. If he had said acouion or acousticon it might have been better, but more difficult to pronounce.
Lee De Forest: Dr. Pupin's opening remarks may serve as an argument why the study of Greek and Latin should be thoroughly introduced into our engineering schools. My knowledge of Greek is almost nil; I knew, however, that 'aud' was of Latin and 'ion' of Greek derivation. But they are both expressive. When we use a term one hundred times a day, it is necessary to have something brief."--"Discussion on 'The Audion: A New Receiver for Wireless Telegraphy', New York, October 26, 1906", Transactions of the American Institute of Electrical Engineers, 1907. |