A Thumbnail History of Electronics


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III. VacuumTubes
The Edison effect, the appearance of an electric current flowing between a heated cathode and an anode in an evacuated tube, was a mysterious phenomenon when it was discovered in 1882; it was not understood how electric current could pass through a vacuum. Thomson's identification of cathode rays as streams of electrons resolved the mystery and led to the invention of the thermionic diode by Fleming. The diode, intended to serve as a rectifier to detect radiotelegraphic signals, had little impact as the coherer, invented by Branly and Lodge, and crystal and magnetic detectors continued to be used. The invention of the triode by DeForest, however, did revolutionize radio communication.


Thomas Alva Edison (1847-1931) was owner or co-owner of a record 1,093 patents.  He alsoedison.gif (8763 bytes) invented the modern industrial research laboratory. In 1882, when one of his engineers, William Hammer,  observed the "Edison Effect" during the course of experiments about the incandescent lamp, Edison, for reasons which he could not  later explain, uncharacteristically did not follow up on the discovery.  But, as he later admitted, at the time he did not even understand Ohm's law.  The Edison effect remained an unexplained curiosity for  fifteen years until the discovery of the electron.


John Ambrose Fleming (1849-1945) had a remarkable career which spanned the first fleming.gif (9094 bytes)seventy-five years of the development of electronics. Fleming was a student of Maxwell’s who later worked as a consultant for Edison and then Marconi. In 1904, following Edison’s observation of the passage of current from the filament to an anode in a light bulb and J.J. Thomson’s discovery that cathode rays consisted of charged particles, Fleming invented and patented the first electronic rectifier, the diode, or Fleming Valve. The device was intended for use in detecting the spark-generated radio waves of the time, replacing the other devices used by the pioneers of radio communication. Fleming was knighted in 1929.


Lee De Forestforest.gif (7887 bytes)(1873-1961), son of a Congregational minister who was president of the Talledega College for Negroes in Alabama, lived a long life full of controversy. He was defrauded by partners, was involved in numerous patent suits, went through two divorces, and once was indicted (but later acquitted) for mail fraud for seeking to sell a worthless device (his audion tube), De Forest held more than 300 patents but is most remembered for initiating the electronic revolution with his 1906 invention of the audion tube, a three-element vacuum tube in which the grid controlled the current,  which made modern radio possible. In 1912 he conceived the idea of cascading triodes to achieve high amplification and also independently discovered regenerative feedback.


William D. Coolidge (1873-1975), an electrical engineering graduate of MIT and the University of Leipzig, joined thecoolidge.gif (8211 bytes) General Electric Research Lab after a brief career in Academia. In 1911, he succeeded in fabricating a ductile form of tungsten which provided the filaments for modern incandescent lamps and also patented a thoriated cathode with improved emission for use in vacuum tubes. In 1913 Coolidge invented a hot-tungsten filament x-ray tube which provided a more penetrating and reliable source for radiology. The "Coolidge tube" became the standard generator of medical x-rays.


Walter Schottky (1886-1976) discovered the random noise due to the irregular arrival of electrons at the anode of thermionic tubes that is called "shot noise" (Schottky effect) in 1914 while studying under Planck in Berlin.schottky.gif (9971 bytes)  Schottky was Swiss, but he was educated and spent his professional career in Germany. In 1919 he invented the first multiple grid vacuum tube, the tetrode. Schottky obtained multiple doctoral degrees, taught at universities from 1920 to 1927, and then worked for Siemans for nearly five decades. He was the first to note the existence of "holes" in the band structure of semiconductors, discovered the type of lattice vacancy known as the Schottky defect, and in 1938 created a theory that explained rectification at a metal/semiconductor interface.


langmuir.gif (8494 bytes)Irving Langmuir (1881-1957), son of a struggling Brooklyn businessman, showed a precocious interest in Science. He received his degrees in Chemistry, but, tiring of the endless round teaching elementary courses and paper grading required of professors, left academia and went to the General Electric Research Laboratory. His work on molecular films won the Nobel Prize in Chemistry in 1932, and his studies on hot filaments in gases became the basis for improvements in incandescent lighting and a huge industry. His discoveries about the emission of electrons from cathodes and their behavior in vacuum tubes  formed the basis for the design of a variety of tube types.


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