This circuit was found in the October 1989 issue of Radio Electronics magazine. It drives an auxiliary relay with the call signal for a possible louder bell.
Found in a Motorola's 1968 documentation, this circuit operates at 16.5 kHz. The output is 5 A....
The operational amplifier is old. The circuit is from an 80's documentation but can be designed...
This tunnel diode circuit was found in American documentation from 1966. The tunnel diode is the...