This circuit was found in an American publication from 1968. The transistors are from the time, but it can be made from modern transistors.
In the figure we have a different configuration for an oscillator with the 555. This circuit was...
This short-range transmitter has the frequency determined by the crystal. The frequency can be...
This very simple amplifier was found in the Philips Databook of 1990. The circuit is suitable for...