This telephone recording circuit was found in the June 1979 issue of Radio Electronics magazine. The components are common at the time and the power is supplied by the power grid.
This power supply with several transistors can supply a current of several amps and a voltage of...
Found in a 1967 EEE, this circuit oscillates at 20 MHz according to the values of the given...
We found this circuit in a 1974 technical documentation. The circuit can be made with BC549...