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.
This circuit, from the 90's, is intended for operation with vinyl record players of the time, as...
Using a zener diode it is possible to change the linearity of the scale of an analog instrument by...
Found in American documentation from the 1980s, this circuit prolongs the ringing of a doorbell or chime...