This trigger circuit was found in an American documentation from the 1980s. The amplifiers used can be replaced by equivalents with characteristics according to the frequency.
This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and...
This small 1 W amplifier uses a Motorola integrated circuit from the 1970s. The integrated circuit...
This is a configuration widely used for oscillators with crystal from 1 to 20 MHz typically. The...