Since its invention in 1904, the two electrodes valve or
diode was used originally only for radio wave detection based
in its capability to rectify the alternating current. However,
in spite such instrinsic operation principle, its appliation
as a reliable rectiying device started only in 1926 when the
first electric powered radio receivers were launched in the
market replacing the ones battery operated.
The first rectifying valves used cathodes coated with oxides.
Since 1914, General Electric in the USA starting to launch
in the market several types of rectifers devices such as:
Kenotron and Tungar. In the mid thirties the first rectifying
valves using indirect heating was developed in the USA. Around
1940, the improvement in the manufacturing technology gave
the birth of the first miniature rectifying valves.