Abstract
The receiving electron tube has been primarily responsible for the modem superheterodyne, with its high sensitivity, high selectivity, automatic gain control, and ease of tuning. In examining the history, one finds an early period of triodes and diodes (1907 to 1927), a second period (1927 to 1936) of indirectly heated cathodes and multigrid tubes, and a third period (1936 to 1960) of close-spaced tubes and VHF operation. The most significant tube concepts are the triode, the multigrid tube, and the indirectly heated cathode, all of which started in the first period. The second and third periods were marked by tremendous advances in the technology of production, and in extensive application of the early inventions to new receiver designs. At present, solid-state devices are gradually supplanting vacuum tubes in some receiver applications, and this trend is expected to continue.
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