Lee De Forest
1873-1961
American Physicist
Lee De Forest introduced a third element into the diode vacuum tube designed by John Ambrose Flemming (1849-1945), providing a means by which a small voltage applied to this element could have a large effect on the current of electrons flowing between cathode and anode. The triode made possible the amplification of weak electrical signals, which in turn made possible the transmission of high quality audio and video signals by radio waves. The transistor, a solid-state device with the electrical properties of a triode, eventually replaced the vacuum tube triode in most applications.
De Forest had a somewhat unusual childhood. His father was a Congregationalist minister and President of the Talledega College for Negroes in Alabama. As a result, the white community ostracized his family, and Lee made his friends among the black children of the town. De Forest attended a private college preparatory school in Massachusetts, and entered the Sheffield Scientific School at Yale University, receiving his bachelor's degree in 1896. He returned to Yale to complete his Ph.D. degree in 1899, submitting a thesis on the reflection of radio waves. De Forest was interested in the transmission of telegraph messages by radio, and improvements made by him on the earlier system were sufficient for him to obtain support from the United States government for his early work.
In order to improve the detection of radio signals, De Forest added a third electrode to thevacuum tube diode invented by John Ambrose Flemming in 1904. The third electrode, placed between the heated anode and the cathode, would eventually make possible for a small electrical signal to modulate, or control, a large current, a capability required for the effective transmission of sound waves by radio and to amplify the small radio signal when received. Before this could be fully developed, however, a number of advances had to be made in the theory of vacuum tube circuits and in the production of high vacuums. Historians now agree that De Forest did not at first appreciate the full range of possibilities afforded by the triode, and viewed it primarily as a technical improvement on the diode. Nonetheless De Forest was happy to take some credit for subsequent developments. He entitled his autobiography Father of Radio and many people regarded him as such.
Lee De Forest. (Library of Congress. Reproduced with permission.)De Forest spent several years in New York City working with the fledgling radio industry and then moved to California where he worked at first for the Federal Telegraph Company. He continued to make many new inventions, receiving over 300 United States patents. His later inventions included an amplifier based on a cascade of triodes and a medical diathermy machine.
De Forest is regarded as a transitional figure in the history of electronics. He was one of the last independent inventors. As a result he was often forced to sell his patents at bargain prices to better-financed corporations, and he lost large sums of money defending his patents. A number of subsequent inventions in the field involved adding additional electrodes to the triode to fine-tune its behavior. Vacuum-tube technology also gave rise to the need for better vacuums and for economical methods of producing them. As a result, large corporations like General Electric and American Telephone and Telegraph began establishing laboratories for fundamental scientific research related to their products. Industrial research became a major employer of scientific talent, increasing the number of scientists and engineers actively at work. Well-financed industrial research would lead in 1947 to the transistor, a solid-state version of triode that would replace vacuum tubes in most applications.
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