Radio Valves

The patents for the very first valve

JOHN AMBROSE FLEMING, D.Sc. - 16th. November, 1904

The first valve The first valve

The first Fleming diode and the patent diagram.

Text of Fleming's British patent 24850.
Text of Fleming's American patent 803,684

Fleming patented the thermionic valve in the U.K. on 16th. November, 1904, when the provisional specification was lodged. The complete specification ws lodged on the 15th. August, 1905 and patent number 24850 was granted on the 21st. September, 1905. In America the patent was lodged on the 19th. April, 1905 and granted on the 7th. November, 1905.

The diagram above was included, identically in both patents. A larger version, suitable for printing, is linked to the image.

Fleming clearly understood the application of his valve (his new term) as a detector of radio frequency oscillations. The illustration above is the very first circuit diagram of a valve radio. Fleming's diode was much more sensitive than the existing coherers.

Although Fleming's valves were constructed using a carbon filament, as used in light bulbs at the time, he did propose the use of metal filaments. In fact any conducting material that could be heated to near the melting point of platinum was stated to be suitable.

He also suggested the use of carbon as an anode material, preventing the patenting of the much later carbon anodes in transmitting valves.

He also described a full wave rectifier, using several valves.

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This page last modified by AJC on Friday, 26-Mar-2010