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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 Porthcurno Telegraph Museum before the institution was renamed the Museum of Global Communications.
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!
This page last modified by AJC - 26-Mar-2010. Last updated 21-Jul-2021