"In electronics, a plate detector (anode bend detector, grid bias detector) is a vacuum tube circuit in which an amplifying tube having a control grid is ...
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operated in a non-linear region of its grid voltage versus plate current transfer characteristic, usually near plate current cutoff, in order to demodulate an amplitude modulated carrier signal. This differs from the grid leak detector, which utilizes non-linearity of the grid voltage versus grid current characteristic for demodulation. It also differs from the diode detector, which is a two terminal device." - (en.wikipedia.org 28.08.2020)