This circuit that generates signals between 1.5 and 2 kHz was found in a documentation from the 90's. The capacitor C1 can be changed to obtain other frequencies.
Texas Instruments ESD122 Electrostatic Discharge Diodes (ESD) can be ordered from Mouser...
This circuit was suggested in a 1976 documentation. We can use the pair BD135 and BD136 on the...
This interesting circuit found in an Elektor from the 90s controls loads in four quadrants of the driving...