Fleming Diode

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A commercial version of the very first vacuum diode

Fleming Diode first made in 1904, this commercial example is probably from before 1910.

The anode with the loop filament just visible.

This is an example of a commercial Fleming diode with a bayonet base, where the filament is connected, and a side entry to the envelope for the anode connection. This one was photographed at the link Porthcurno Telegraph Museum . A visit is strongly recommended for those with an interest in old technology. Among the exhibits are two working spark transmitters, one a replica of the Titanic radio room, as well as masses of submarine cable telegraph equipment.

The very earliest examples did not have bases fitted. All were bright emitters with carbon or tungsten filaments. They were used as detectors of radio frequencies. Here is the original with the text of Fleming's original British patent and his original US patent. . Figure 1. is the earliest circuit diagram of a valve radio!