Dynatron oscillator
![Dynatron vacuum tube signal generator, 1931. It covered the range 1.8 to 15 MHz. The circuit was used in signal generators due to its frequency stability, which was compared to crystal oscillatorsThe dynatron oscillator circuit was also used as the local oscillator in superheterodyne radio receivers, such as this 1931 Crosley model 122 seven tube radio.](/Images/godic/202502/17/Dynatron_signal_generator_19310455.jpg")
![](/Images/godic/202502/17/Crosley_122_Super_Buddy_Boy_radio_receiver_19310455.jpg")
![Dynatron tube, the first tube to produce dynatron oscillations, invented by Albert Hull in 1918.[2] It saw little use since the triode and the tetrode, invented in 1926, proved capable of dynatron oscillations also.](/Images/godic/202502/17/Dynatron_tube0455.png")
![Dynatron oscillator circuit](/Images/godic/202502/17/Dynatron_oscillator_circuit.svg0455.png")
In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission. It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes.