English: A replica of one of the bulbs with which
Thomas Alva Edison discovered the
Edison Effect (
thermionic emission) in the early 1880s. Made by Clayton H. Sharp in 1921 as an experiment to see if Edison's bulb could be used like a
Fleming valve as a detector in a radio receiver to rectify radio waves. It worked.
It consists of an Edison incandescent light bulb, an evacuated glass bulb with a hairpin shaped bamboo carbon filament, with an additional platinum plate (visible between the arms of the filament) attached to wires emerging from the base of the bulb. A current through the filament heated it white-hot. Edison discovered that the hot filament emitted negatively-charged particles (later discovered to be electrons) an effect that was called the Edison effect. He demonstrated this by applying a separate voltage between the filament and plate. When the plate had a positive voltage, the electrons were attracted to it and a current flowed through the tube from filament to plate. When the plate had a negative voltage, the electrons were repelled so no current flowed through the tube. Edison found no practical use for this effect, but in 1904 John Ambrose Fleming invented a similar tube called the Fleming valve which was used to rectify radio signals in the first radio receivers, which evolved into the diode vacuum tube.
Alterations to image: partially removed aliasing artifacts (crosshatched lines in background) due to scanning of halftone photo using FFT filter in GIMP.