We found this circuit with duty cycle adjustment in the May 1988 Radio Electronics magazine. The source must be symmetrical, and the frequency given by R3 and C1.
Indicated by Popular Electronics to be used with a car headlight, this circuit can also have...
In this circuit of a 1970s publication, data from the coil to oscillate at the desired frequency...
This circuit was obtained from a Philips documentation from 1968. The transistors can be replaced...