| In 1883, Thomas Edison, working on methods to keep the
early light bulbs from blackening, discovered what is now called the Edison
effect. These tubes had a carbon filament working in a vacuum, and the
filament slowly evaporated. Edison tried placing a metallic plate inside
the bulb, and discovered that when it was positive with respect to the
filament, a current appeared to flow through the vacuum. This phenomenon
was investigated thoroughly by the British physicist and electrical engineer,
Ambrose Fleming, who devised a two-element vacuum tube known as a Fleming
valve. This diode could be used as a rectifier and a detector.
The DeForest Audion was the first three-element (triode)
vacuum tube. Lee DeForest (1873-1961) received his doctorate in 1899 from
Yale, working on a problem in wireless telegraphy. He developed the audion
in 1907. Between the filament and the plate he inserted a grid; varying
the (negative) potential on the grid controlled a considerable current
from the filament to the plate. This is the essence of amplification, and
the electronics industry is the consequence.
By 1910 DeForest was able to broadcast part of a performance
of the Metropolitan Opera, featuring Enrico Caruso. |
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