De Forest’s Audion tube

Lee de Forest (1873-1961), an ambitious experimenter, was always on the hunt for profit. He attempted numerous business ventures, often unwisely chose his business partners, and frequently was involved in litigation. He filed more than 300 patents over more than 50 years of invention, but his triode vacuum tube or “Audion,” would be his most important contribution to modern electronics. De Forest’s Audion tube patents (1906, 1915) were at the heart of decades of patent litigation.

In 1911, de Forest faced bankruptcy. After yet another failed business venture, he had asked Cyril Elwell for a job at Federal Telegraph Company in Palo Alto. De Forest had helped Federal Telegraph with installations in San Francisco (1910) and Los Angeles (1911), and was well known by Federal’s small staff. Elwell teamed de Forest with Charles Logwood and Herbert Van Etten — an accomplished telephone engineer — and asked them to develop a more efficient telegraph key using a vacuum tube detector for reception. The result was a triode vacuum tube that could amplify and oscillate radio waves; it became the basis of radio transmission.

De Forest “was an unusual man,” Fuller later recalled, “possessed of an uncontrollable drive to experiment.” He was also extremely secretive, reluctant to share his team’s work with Federal’s electrical engineers. Fuller later questioned whether de Forest actually understood the science behind the Audion’s redevelopment. Nevertheless, de Forest took credit for the new Audion, waiting until after Elwell left the company to file for patent rights.

de Forest dual filament Audion, 1908

This rare dual tantalum filament de Forest Audion was handmade by H. W. McCandless & Co. of New York (an automotive light bulb maker) in 1908, the only year double filament audion tubes of this type were made. The glass tube was mated to a standard candelabra light bulb screw base. The grid is the usual zig-zag formation (made by bending wire between nails hammered into a piece of wood). The single plate has a single anchor wire. The filament supports come up from the screw base, rather from a glass press. The contact was soldered externally to the base to make contact. The base insulation is glass, rather than porcelain. The cap is tarred over, covering the exhaust tip.

de Forest Hudson filament Audion, 1914

By the time this 1914 de Forest Audion was made for the U.S. Navy, the triode vacuum tube served as an amplifier of audio and an oscillator for transmitting. This globe-shaped Audion was handmade in the shop of H. W. McCandless and Co, New York, in 1914. Although McCandless had been using the globe shape since about 1908, it is the bulb’s double “Hudson” filament that dates it to 1914. The Hudson technique, developed that year, required a tungston wire to be wrapped around a tantalum filament (later the tantalum filament was dipped).

In this bulb, both tungsten and tantalum filament are, remarkably, intact. Hundreds of tubes like this one were sold to the U.S. Navy between 1914-1915 (not for commercial use), all made by McCandless. On the exterior of the candelabra base, the second filament is protected by string and rubber band, suggesting the second filament was not used. The single plate, or wing, does not have clipped edges. Two attached paper labels note its patent number and date, and that its production was not for commercial use.

de Forest double wing Audion amplifier, c. 1915

This de Forest 3.5 volt, double wing Audion amplifier has two grids and two “wings” set on either side of the tantalum filament. Double Audions, a 1909 refinement to increase the sensitivity of the tube and gain greater energy output, were sold at a higher price than the original. This is an improved version, made in 1915 under the supervision of Robert F. Gowen at the High Bridge Laboratory.