Patent Battles

Experts seem to differ as to whether de Forest actually began with Fleming's diode and then used the gas flame experiments to try to fight off the accusation of infringing Fleming's patent, or whether de Forest's account is the truth. De Forest was always sensitive to the possibility of a suit for infringement of Fleming's patent, which was owned by the Marconi Company. When the suit did come, Marconi won.. Some accept de Forest's explanations of how he made his invention as being the way it was, others see them virtually as disinformation designed to protect himself against this possible suit.

The triode was invented in 1906 and a patent filed in January 1907. De Forest seems to have regarded it as a finished product and did not seek further improvements. He turned his attentions to radio telephony. For years the triode was simply another radio detector, sometimes better, sometimes worse than the more popular crystal or electrolytic detectors.

What transformed the triode into the basis of electronics were the improvements made by industrial laboratories following the discovery of how to use it to amplify and oscillate. These circuit inventions were made independently by several people in 1912 and 1913, de Forest being one of them. The arrival of the amplifier was of great significance to the telephone companies as well as the those involved in radio telegraphy. AT&T bought the repeater rights to the triode for $50 000 in 1913 and later the radio rights as well.

The value of the triode as an oscillator was that it could be used to generate continuous electromagnetic waves for radio transmitters. Four men contested the patent rights to the invention, with de Forest eventually winning the legal battles. The longest patent litigation in American radio history was that between de Forest and Edwin Armstrong over the invention of the feedback or regenerative circuit. When Armstrong won the first round in 1917, de Forest sold his patents and any future valve inventions he might make to AT&T for $250 000. From then on he seemed to lose interest in radio, turning instead to talking pictures. The final legal judgement however went to 7 de Forest, with engineers generally feeling that Armstrong had been let down.

Success

Once the triode had found important uses as an amplifier and oscillator, industrial scientists were quick to understand its mode of operation. De Forest's gas was evacuated to produce a high-vacuum device and a filament life of 1000 hours was achieved in 1913. Oxide-coated filaments8 increased emission and more new circuits were invented such as the push-pull amplifier9 (E.H. Colpitts, 1912) and the Colpitts and Hartley oscillators. The First World War provided further stimulus for improvements and use. A somewhat similar path was followed in Europe where Robert von Lieben patented first a diode (1906) and then a triode (1910).

In 1911, when de Forest's company was in severe financial difficulty, he took a job with the Federal Telegraph Company in Palo Alto, California. California then became his home.

Above all, de Forest was a prolific inventor, not a businessman nor a scientist. Amongst his other patented inventions were a high-frequency surgical cautery device10, several types of microphones and loudspeakers, and stereoscopic and large-picture television. Naturally he received many medals and decorations but the decision not to award him the Nobel Prize is said to have left him heartbroken. He seems to have had the knack of inspiring intense loyalty11 in some people, but antipathy in others.

For the last two years of his life illness kept him bedridden, almost totally incapacitated, and financially drained. He died on June 30, 1961, at his home in Hollywood, California, in his 88th year and just four years after his last patent was issued. His fourth wife, Marie, survived him. He was one of the last great individual inventors.

Task I

Tell about Lee de Forest’s business activity.

Task II

Tell the history of triode development and improvements.

Task III

Speak on de Forest’s inventions.

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