This circuit uses a capacitor that depends on the frequency of the crystal. We found it in a 1967 documentation. The maximum frequency is around 100 kHz.
This circuit was used to regulate the speed of small DC motors of cassette recorders. However, if the...
This excellent 30 W tube amplifier appeared in the April 1963 Radio Electronics magazine that...
This circuit was found in a 1980s documentation. It shows how to obtain a bistable with the 555 by...