This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by BC548. The relay must have 100 mA of maximum current.
Found in a 1980s telecommunications documentation, this balanced modulator circuit uses...
This circuit was found in a 90’s 303 Circuits. The components are from the period and the heating...
This simple receiver that works with only 1.5 V, was found in a 1987 documentation. The integrated...