Found in the July 1994 Electronics Now magazine, this circuit drives a relay up to 12 V depending on the power supply. The transistor can be general purpose.
The frequency of this type is oscillator is given by the RC network. Calculations can be found in...
This configuration, which appears in other points of this section and website with small...
This circuit is from the 1960 Mullard transistor manual. The transistors are germanium from the...