Lee De Forest

Lee de Forest was one of the most important of the inventors of radio and electronic technology, a formally educated scientist whose inventions touch every life. He is most known for his pioneering work with the vacuum tube, first as a detector of radio waves, then as an amplifier for long distance telephone calls, and finally as the major technology of the radio transmitter, still in use today.

Lee de Forest was born in Council Bluffs, Iowa (USA) on August 26, 1873. De Forest was the son of a Congregational minister. His father moved the family to Alabama and there assumed the presidency of the nearly bankrupt Talladega College, a small black school. Ostracized by citizens of the white community who resented his father's efforts to educate blacks, Lee made his friends from among the black children of the town and, together with his brother and sister, spent a happy although sternly disciplined childhood in this rural community.

As a child he was fascinated with machinery and was often excited when hearing of the many technological advances during the late 19th century. By the age of 13 he was an enthusiastic inventor of mechanical gadgets such as a miniature blast furnace and locomotive, and a working silverplating apparatus. But while de Forest grew up in the deep South, his education was formal and upper class. Lee de Forest's father hoped that his son would follow in his footsteps. In order to be trained for this calling, de Forest left Alabama to attend Mt Hermon boys school in Massachusetts. His life at school was hard, with chores as well as academics, plus work to supplement his scholarship. Besides, he was not well-liked there. Biographers report he was extremely concerned with getting recognition from his peers, an issue which lasted throughout his life. Alas, he only won acknowledgement as "homeliest boy in school." Despite this, he was confident. During school, de Forest had tried to get money and fame by inventing things he might sell or enter in contests, but none were great successes.

His father had planned for him a career in the clergy, but Lee insisted on science and, in 1893, enrolled at the Sheffield Scientific School of Yale University, one of the few institutions in the United States then offering a first-class scientific education. Frugal and hardworking, he supplemented his scholarship and the slim allowance provided by his parents by working at menial jobs during his college years, and, despite a not too distinguished undergraduate career, he went on to earn the Ph.D. in physics in 1899.

His first job was with the Western Electric Company in Chicago, where, beginning in the dynamo department, he worked his way up to the telephone section and then to the experimental laboratory. While working after-hours on his own, he developed an electrolytic detector of Hertzian waves. The device was modestly successful, as was an alternating-current transmitter that he designed.

A poor businessman and a poorer judge of men, de Forest was defrauded twice by his own business partners. In 1902 de Forest joined a Wall Street promoter named Abraham White and formed the de Forest Wireless Telegraph Company. Among their early customers were the War Department and the Navy. In order to dramatize the potential of this new medium of communication, he began, as early as 1902, to give public demonstrations of wireless telegraphy for businessmen, the press, and the military. Under the guidance of White, a public offering of stock was made, public demonstrations were held, and radio equipment was sold. But characteristic of his entire career, the hyperbole surrounding the company was greater than its actual value, and while de Forest continued to invent, he was apparently unaware that White was engaging in less than ethical business practices. By 1906 his first company was insolvent, and he had been squeezed out of its operation.

Deforest's inventions changed the world

During his lifetime, Lee de Forest received over 180 patents. His most significant was the 3 element vacuum tube. In 1921, De Forest invented a way of recording sound on movies. He started a company, the De Forest Phonofilm Corporation, but he couldn't convince the film industry to try using sound.  Once film makers finally came around, several years after the Phonofilm Company folded, they decided to use an entirely different method.  (Though some time later movies actually began to use the method De Forest originally proposed.) 

In 1907 he patented a much more promising detector which he called the "Audion"; it was capable of more sensitive reception of wireless signals than were the electrolytic and Carborundum types then in use. It was a thermionic grid-triode vacuum tube — a three-element electronic "valve" similar to a two-element device patented by Sir John Ambrose Fleming in 1905. By 1906 de Forest had modified Fleming's valve by adding a grid to control and amplify signals, and called his device the Audion. At the right is the original Audion patent, dated January 15, 1907. The Audion was used as a detector of radio signals, an amplifier of audio and an oscillator for transmitting.

Audion Patent, January 15 1907
and a real Audion tube above it







Audion sheme





De Forest Audion vacuum tube, 1906




De Forest valve, 1918-20



Electronic devices based on De Forest's Audion

1) Audion Receiver, 1907




2) Radiotelephone, 1907 deforest_radiotelephone1907




3) De Forest Diathermy Generator, 250W, 18 MHz



Source: http://people.clarkson.edu

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