Fleming_valve.jpg
Summary
Description Fleming valve.jpg |
English:
Early
Fleming valve
or
thermionic diode
, the first
vacuum tube
, invented by
John Ambrose Fleming
in 1904. It consists of an evacuated glass envelope containing two electrodes: a cathode in the form of a
filament
heated by a separate current, which emitted electrons, and a metal plate
anode
, which in this tube is a sheet metal cylinder surrounding the filament. The Fleming valve was used as a
detector
in early radio receivers, to extract the audio modulation (sound) from the radio frequency
carrier wave
. The incoming radio signal was applied across the tube. On the positive half cycles of the wave when the anode was positive with respect to the cathode, the negative electrons are attracted to the anode, causing a current through the tube, while when the anode is at a negative potential with respect to the cathode the electrons are repelled and no current flows. Thus the Fleming valve was able to rectify the alternating radio current to a pulsing direct current (DC). It was used in receivers built by the Marconi Co. until about 1920, when the Audion (triode) replaced it.
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Date | |
Source | Retrieved December 30, 2015 from Gerald F. J. Tyne, "The Saga of the Vacuum Tube" in Radio News magazine, Ziff-Davis Publishing Co., New York, Vol. 30, No. 1, July, 1943, p. 31, fig. 18 on http://www.americanradiohistory.com |
Author | Gerald F. J. Tyne |
Licensing
Public domain Public domain false false |
This media file is in the
public domain
in the
United States
. This applies to U.S. works where the copyright has expired, often because its first
publication
occurred prior to January 1, 1929, and if not then due to lack of notice or renewal. See
this page
for further explanation.
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This image might not be in the public domain outside of the United States; this especially applies in the countries and areas that do not apply the
rule of the shorter term
for US works, such as Canada, Mainland China (not Hong Kong or Macao), Germany, Mexico, and Switzerland. The creator and year of publication are essential information and must be provided. See
Wikipedia:Public domain
and
Wikipedia:Copyrights
for more details.
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