Tuesday, August 26, 2014

Lee De Forest and the Audion

Lee De Forest with two of his tubes
On August 26, 1873, American inventor Lee de Forest was born. He is credited more than 180 patents. In 1906, de Forest invented the Audion, the first triode vacuum tube and the first electrical device which could amplify a weak electrical signal and make it stronger, making radio broadcasting, television, and long-distance telephone service possible, among many other applications.

Lee De Forest knew that he wanted to become an inventor at very early age. It is known that he performed many experiments during his childhood and created several electrical and mechanical devices. The young De Forest wrote a letter to his father: "I intend to be a machinist and inventor, because I have great talents in that direction. In this I think you will agree with me. If this be so, why not allow me to so study as to best prepare myself for that profession? In doing this it would be much better to prepare myself for and take the Sheffield Scientific course". Shortly after, he enrolled at the Sheffield Scientific School at Yale University in Connecticut in 1893, where he earned his Ph.D. with a dissertation on radio waves [1].

De Forrest was hired by Western Electric, where he devised dynamos, telephone equipment, and early radio gear. He used the wireless telegraph which had earlier been introduced by Marconi and searched for a better detector or receiver and patented a device he called the 'responder'. The inventor started his own business in 1902 called 'De Forest Wireless Telegraph Company', selling selling radio equipment and demonstrating the new technology by broadcasting Morse code signals. However, he resigned as its president four years later. While Lee De Forrest worked on the improvement of the wireless telegraph equipment, he modified the vacuum tube invented by John Ambrose Fleming and designed the Audion, and he used it to detect or receive code and voice messages. In the book, 'Lee de Forest, King of Radio, Television, and Film' it was said that "the patentable differences between this invention and that of Fleming are de Forest’s addition of the second battery between the plate and the earphone, called a 'B' battery, and the use of a telephone earphone instead of the galvanometer. These two very significant changes result in the 'hearing' of a signal as opposed to Fleming’s 'seeing' it using a visual indicator. These differences mean that only the de Forest version will be able to 'hear' the audio from the imminent invention of the radiotelephone" [1,2].

The inventor published the first known writings on how music could be send into homes using the wireless telephone, or the radio. He used his audion detector as a radio receiver and his audion amplifier to make small signals louder, and the oscillating audion as a transmitter. He set up a radio station in the Bronx in 1916, but without any financial success. In the 1920s, he worked on a system for producing motion pictures with sound, but unfortunately, the film industry became not really interested in his technology. However, when the industry later on adopted the concept of sound on film, a process very similar to De Forest’s was used [3].

For his contributions, Lee De Forest was awarded the 1922 Medal of Honor of the Institute of Radio Engineers and the 1946 Edison Medal from the AIEE. During his life time, the inventor filed almost 200 patents, but passed away as a poor man in 1961 [3].

At yovisto, you may be interested in a lecture by ... on the book 'Lee De Forest - King of Radio, Television, and Film'



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