This circuit was originally recommended to give the call signal on intercoms. However, it can be used with other applications. The circuit is from 1978 documentation. The transistor may be the BC548.
Found in a 1966 publication, this circuit is a simple version of a field strength meter. The diode...
This circuit of 1965 documentation makes use of a tunnel diode to retard a pulse without...
Found in ancient American documentation this circuit uses semiconductors from the thyristor family such as...