Plate detector circuits were commonly used from the introduction of indirectly heated cathode tubes in the late 1920s until the start of World War II . As R . F . tubes became more sensitive, grid-leak detectors ( which are more sensitive than plate detectors ) became less practical.
22.
As with the standard plate detector, the device is biased almost completely off, and positive-going halves of the input signal cause the device to quickly charge C 2 up from the positive power supply but the capacitor can only be discharged slowly via R 1, so the circuit acts as a peak detector.
