English: Schematic diagram of a "Crystodyne" negative resistance zinc oxide point-contact diode oscillator invented by Russian scientist Oleg Losev in 1923, published in an American radio magazine. Losev used zinc oxide diodes to build the first semiconductor amplifiers and negative resistance devices, which he used to construct solid state radio transmitters and regenerative and superheterodyne radio receivers, 25 years before the invention of the transistor. However Losev's achievements were overlooked because of the popularity of vacuum tube technology, and were forgotten until they were rediscovered in recent decades.

This is the schematic diagram of the oscillator shown in Crystodyne zincite oscillator - top.png and Crystodyne zincite oscillator - side.png, built by Hugo Gernsback in New York to Losev's instructions. It can produce radio frequency output up to a few megahertz. The active device is the "cat's whisker" diode D, consisting of a crystal of zincite (zinc oxide) with its surface lightly touched by a steel wire on an adjustable arm. It is biased into its negative resistance region by a DC voltage of 4 - 30 volts applied by battery B and potentiometer R. The negative resistance of the diode excites oscillation in the series tuned circuit, consisting of capacitor C₁ and variometer inductor L₁. Before operation, a sensitive contact point must be found on the surface of the crystal. To do this switch K is turned to the upper position, which switches a second tuned circuit in, L₂ and C₂ which oscillates at audio frequency. The wire is dragged across the surface of the zincite crystal until a tone is heard in the earphones, indicating the oscillator is working. Then switch K is turned back to the lower position, switching the RF tuned circuit in. The component values from the source are R = 3 kΩ, L₁ = 5 mH, C₁ = 10 pF, L₂ = 1 H, C₂ = 2 mF. With these values the frequency of oscillation is approximately

${\displaystyle f={1 \over 2\pi }{\sqrt {1 \over L_{1}C_{1}}}=2.3\;{\text{MHz}}}$

Caption: "Diagram of the oscillating crystal circuit. As can be seen, the hookup is similar to an arc transmitter." Alterations to image: Added labels B and D