How the Radio Valve Grew Up

Radio Record, Volume V, Issue 2, 24 July 1931, Page 3

How the Radio Valve Grew Up

An intimate story of the development of the radio valve from the first crude rectifiers to the modern multi-mu valve of to-day, told by that great pioneer ‘of radio

Dr.

Lee de

Forest

y ITHOUT the audion, or na three-element valve, there ould be no radio industry. At least, the tadio industry would not be catering to the public at large, supplying millions of radio sets and tens of millions of radio valves each year, and maintaining over six hundred broadcasting stations pouring forth a steady stream of entertainment and enlightenment-and considerable advertising. Rather, there would be a relatively small communication business for the handling of marine and trans-oceanic traffic. In the final analysis, it is the, valve that has brought about simplified and practical radio. Hence, in the production of valves-the veritable footlights of the world’s stage-is reflected the rapid progress of the radio art, science and industry. The giant valve industry of to-day came about through an accident. Many of- my readers may recall the story. However, for the.'newer members of the radio fraternity, I may be permitted to repeat ‘the brief details. .Back in 1904, while engaged as associate editor of "The Western Electrician," I spent my spare time in wireless experiments., Among my possessions was a large: jump-spark coil. One evening, I noticed that each time the spark jumped the gap, -the near-by Welsbach mantle flickered. It occurred to me that the Hertzian or wireless waves. must have some influence on the particles of heated gas in the Welsbach -ymantle. Perhaps, after all, this might be the sis for a new wireless detector, which was sadly needed in those days of crude co-herers. And so I looked into the proposition. The first gaseous detector took the form of a standard Bunsen burner, with a troughlike electrode containing common table salt...

and a piece of platinum wire about it, placed in the blue flame of the burner. A battery * and headphone were shunted across the flame, ‘through the electrodes. The salt was used to improve the action. The antenna and ground were. connected to the two electrodes. Fair results were obtained from this detector. However, marine wireless was our main consideration in those days. And since there was no illuminating gas available on shipboard, I decided to use a glass bulb filled with gas, and a heated filament as the source of heat, operated entirely by batteries. One discovery led to another. The fact that much of the signal energy passed through the battery and headphone instead of through the gaseous medium led to the idea of a separate and distinct path for the wireless signal, and in turn the third element made its appearance, first as a metal band around the outside of

the glass bulb, then as a second plate quite close to the first or real plate, and finally in the shape of 2

zigzag length of wire which, for want of @ better name, I called the grid. So by 1906 I had developed the audion or three-element valve, in all respects similar to the standard radio valve of to-day. The next step was to manufacture the audion, At first I tried to interest the large lamp companies, since the audion was very. much in their line, being a modified electric lamp. But to no avail. The lamp companies had no time to bother with this fantastic experiment. Somewhat of a contrast, to be: sure, with present-day conditions when so many lamp companies have rushed into the valve business, I succeeded in interesting one McCandless, a producer of miniature electric lights. located

on Park Place, New (Continued on ». 29).

How the Valve Grew Up (Continued from page 3.) York. © McCandless’s became the first yalve plant. His men, skilled glassblowers that they were, made the early audions, which were. sold mainly to wireless experimenters for use ag a detector. The audion was "supplied with a wooden cabinet containing flashlight batteries for the "B" circuit, and with binding-posts and switches for the necessary connections. According to one of our early advertisements: "The audion detector is operated by heated gases, employs 4 local battery and is complete with switches, batteries, rheostat and necessary connections. It is fully protected by U.S. patents Nos. 879,532, 979,275 and others granted to Dr. Lee De Forest and held ‘by the Radio Telephone Company. It is pronounced by experts to be the very best detector obtainable anywhere. Renewal audion bulbs may be secured, in exchange for old or broken ones, for 8.50 dollars or 5.00 dollars each. All valves are tested before shipment, but the ‘X’ or 5.00 dollar bulbs are tested for the maximum possible sensitiveness. With the audion you can easily

increase your range from 50 to 100 per cent." Our first audions made use of tantalum filaments. Usually a double-loop filament was employed, with three pigtail leads, so that one or the other loop might be used. When one loop or filament burned out, another was still available, thereby giving the short enough life of those audions a double span, so to speak. The valves were quite gassy. The plate voltage had to be delicately adjusted so as to be set at the most critical value. If increased beyond a given point, the valve would suddenly light with a purplish glow, and the signals would become garbled. _In time, the audion came into use for telephone purposes. It was in 1915 that the American Telephone and Telegraph Company, employing the De Forest amplifier, inaugurated the first transcontinental telephone services between New York and San Francisco. The same year that organisation, using my "oscillions," or oscillating audions, made successful wireless telephone tests between Arlington, Va., and the Eiffel Tower in Paris, and again with Pearl Habour, in Hawaii. So thoroughly convinced were wire and wireless men of the value of the audion or three-element valve

that the device received no end of re search and engineering development. In 1917 I entered into an agreement with the American Telephone and Telegraph Company, whereby that organisation secured certain rights under the audion patents and whereby sufficient audions might be made available te the Army and Navy for radio communieation during the World War. ‘The telephone company, in turn, re-licensed others to make and use the audion, so that to-day every reputable valve manufacturer is a re-licensee under the DeForest audion patents: Until the dawn of broadcasting, vacuum. valves were made by means of more or less laboratory equipment, The relatively small volume of production could be cared for by glassblowers, with a minimum of machinery. The existing lamp-making machinery was found ample, particularly since the tolerances for yacuum tubes were fairly wide. The prices asked for valves were such that they could be made piecemeal and without much regard for cost. But with the inauguration of broadcasting and the sudden demand for valves by the public at large, the making of vacuum valves. became @& real industry, No longer was it @ question of supplying thousands of valves. Rather, it was a matter of supplying millions of valves to operate the sets in millions of homes. For the first year or two of broadcasting there existed a market shortage of valves. There were times when the list prices meant nothing as regards a maximum. Valves often actually sold at a premium, because of the greater demand than. supply. By degrees, the valve industry geared itself to the demands. Automatie equipment was. installed in the better plants. The skilled glassworker was replaced by the automatic machine, with its batteries of blue gas flames, its mechanical arms and fingers, and its constant merry-go-round operation for continuous production. Girl operators came into the industry, mounting and spot-weilding the metal parts in place on the glass stem, and loading and unloading the automatic machines, followed by testing, inspection, wrapping and packaging. If one will glance at an early DeForest audion, with elements spaced j-inch or more apart, then at the first 201 valve of early broadcasting days, and again at the present -27 heater type ac. valve, and the more complicated fourelement valves, one is immediately struck with the growing delicacy of valve construction. The greater ac curacy of automatic machinery made possible closer tolerances and more accurate valves. (With acknowledgments. to "Radio News.’’)