We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
This analog volt-ammeter was found in an Electronics World of 1968. It makes use of a 0-1 mA...
This is one of the many possible siren configurations for the 555 integrated circuit. We found it in...
This circuit was found in an Electronics World magazine from 1990. The circuit can be mounted...