English: An experimental negative resistance oscillator using a zincite point-contact semiconductor junction. This technology, discovered by William Henry Eccles and G. W. Pickard around 1908 but independently discovered and developed by Russian radio researcher Oleg Losev in 1923 and dubbed "Crystodyne" by Hugo Gernsback, was the first solid-state oscillator and the first observation of negative resistance in semiconductors. Losev used it to build the first solid-state amplifiers, regenerative radio receivers, and transmitters, 25 years before the transistor. However the technology was overlooked because of the success of vacuum tubes, and after 10 years Losev stopped pursuing it and it was forgotten.

The circuit, built in the laboratories of Gernsback's magazine Radio News to Losev's specifications, was a radio frequency oscillator using a cat whisker detector (9) made of a crystal of zincite (zinc oxide) with its surface lightly touched by a slender steel wire on an adjustable arm. It required a DC bias voltage across it of 4 to 30 V, provided by a battery attached to the clips (11). Only certain sites on the crystal surface had negative resistance and the crystal was very sensitive to the pressure of the contact, so a usable contact point had to be found before each use. To adjust the crystal, switch (7) connected a second tuned circuit with a lower resonant frequency, making it oscillate in the audio range. The cat whisker wire was dragged across the crystal surface until the crystal began oscillating, producing a musical tone in the earphones, indicating that a spot with negative resistance had been found. Then the switch was thrown, connecting the crystal to a second tuned circuit which oscillated at radio frequency. The labeled parts are: (1) variometer, (2) variable tuning capacitor, (3) honeycomb tuning coil, (4) 5 pf DC blocking capacitor, (5) choke, (6) 3kΩ potentiometer to adjust crystal bias, (7) switch to connect crystal to adjustment circuit. (8) resistor, (9) zincite-steel crystal detector, (10) earphone connectors, (11) battery connectors.