Grid-leak detector

Example of single tube triode grid leak receiver from 1920, the first type of amplifying radio receiver. In the left picture the grid leak resistor and capacitor are labeled.
A grid leak resistor and capacitor unit from 1926. The 2 megohm cartridge resistor is replaceable so the user can try different values. The parallel capacitor is built into the holder.

A grid leak detector is an electronic circuit that demodulates an amplitude modulated alternating current and amplifies the recovered modulating voltage. The circuit utilizes the non-linear cathode to control grid conduction characteristic and the amplification factor of a vacuum tube.[1][2] Invented by Lee De Forest around 1912, it was used as the detector (demodulator) in the first vacuum tube radio receivers until the 1930s.

  1. ^ Cruft Electronics Staff, Electronic Circuits and Tubes, New York: McGraw-Hill, 1947, p. 705
  2. ^ H. A. Robinson, "The Operating Characteristics of Vacuum Tube Detectors", Part I, QST, vol. XIV, no. 8, p. 23, Aug. 1930