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UNITED STATES EARLY RADIO HISTORY
THOMAS H. WHITE | |
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Expanded Audion and Vacuum-tube Development (1917-1924)
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The wartime consolidation of the radio industry under government control led to important advances in radio equipment engineering and manufacturing, especially vacuum-tube technology. Still, some would look toward the day when vacuum-tubes would be supplanted by something more efficient and compact, although this was another development which would take decades to be realized. WARTIME ADVANCES During World War One the military took over control of the entire U.S. radio industry, and in conjunction with the major electrical firms made great strides in radio engineering using vacuum-tubes. In addition, wartime work exposed thousands in military service to the changes which were taking place, especially with respect to vacuum-tube equipment. The Vacuum Tubes entry by Major General George O. Squier, in the Signal Corps section of the 1919 edition of War Department Annual Reports, reviewed the advances made in vacuum-tube manufacturing and engineering from 1917 to 1919, with the prediction "That vacuum tubes in various forms and sizes will, within a few years, become widely used in every field of electrical development and application is not to be denied." And shortly after the war ended articles started to appear that showed a comprehensive scientific understanding and explanation of the design and operation of vacuum-tubes, for example L. M. Clement's The Vacuum Tube as a Detector and Amplifier (extract), from the April, 1920 issue of QST. H. Winfield Secor's The Versatile Audion, which appeared in the February, 1920 Electrical Experimenter, reviewed the advances taking place in thirteen areas of vacuum-tube engineering. In April, 1919 AT&T, employing vacuum-tube versatility from six of Secor's categories, transmitted speeches and entertainment by phone lines and radio to a Victory Liberty Loan drive, as reported by Speeches Through Radiotelephone Inspire New York Crowds, from the May 31, 1919 Electrical Review. By 1922 vacuum-tubes had been firmly established as a major technological advance, and the Vacuum Tubes chapter of William C. Ballard, Jr.'s 1922 Elements of Radio Telephony reviewed the device and its construction. SEARCH FOR SOLID-STATE ALTERNATIVES In spite of their impressive versatility, vacuum tubes still had significant drawbacks -- they were expensive, had to be replaced when they burned out, and required heavy batteries for the relatively strong electrical currents they needed in order to operate. So some looked for a simpler, more compact device that would perform the same functions, for example, Hugo Gernsback, who, in Developing the Radiophone, from the December, 1919 Radio Amateur News, suggested that experimenters "should look for substitutes of vacuum tubes" which would be worth "a king's ransom for the patent". One promising line of investigation was the "oscillating crystal". Since 1906, crystals had been used as rectifiers for simple detectors, although even in this basic role they were often temperamental and prone to getting out of adjustment when jarred. And to fully replace vacuum tubes, oscillating crystals would have to work in circuits that produced steady electrical oscillations, for amplifying signals and producing continuous-wave transmissions. There were tantalizing hints that some day this might be possible. In March, 1920, QST magazine included a short note in the Strays column about a simple, low-power oscillating crystal circuit designed by Greenleaf W. Pickard. (Pickard later noted that the basic idea dated back to work done by Dr. W. H. Eccles in 1910). Then, in late 1924, there was a brief flurry of excitement, as Hugo Gernsback announced A Sensational Radio Invention in the September, 1924 Radio News, proclaiming that Russian O. V. Lossev's work on oscillating crystal circuits meant that "The crystal now actually replaces the vacuum tube". The same issue of the magazine included an article with simple construction projects, to provide hobbyists a chance to experiment with The Crystodyne Principle. Gernsback predicted that, although development was admittedly still in the experimental stages, within three-to-five years receivers using oscillating crystals in place of tubes would go on sale to the general public. However, it turned out that for the next few decades radio enthusiasts would have to make do with incremental improvements in vacuum tube design -- tubes that required less current, lasted longer, and could run on household electrical current instead of storage batteries. It was only when a deeper knowledge of solid state physics made it possible to refine oscillating crystals into much more practical and reliable "transfer resistors" (transistors) that, beginning in the mid-1950s, the lightweight radios running on flashlight batteries envisioned by Gernsback finally became available to the general public. (In its October, 1948 issue, QST magazine reviewed the development of the transistor by Bell Laboratories, which included the construction of a simple superheterodyne receiver, in The "Transistor"--an Amplifying Crystal, noting that "These clever little devices are well worth keeping an eye on.") |
| "There has arisen within the last few year a new and important type of sustained radio frequency generator, namely, the hot cathode vacuum rectifier, usually with three internal electrodes. As will appear, the ease and certainty of control of circuits formed by pure electron streams in a vacuum has rendered these devices suitable not only for use as generators, but also amenable to telephonic modulation and control of radio frequency output. Since the mode of action of the devices described here is still, in many cases, under judicial consideration in the courts of this country, we shall confine ourselves to giving without comment the explanations advanced by various investigators."--Alfred N. Goldsmith, Radio Telephony, 1918. |