Found in a 1980s documentation, this amplifier uses an integrated circuit that is not easy to obtain now as it is of the era. The circuit is intended for FI ceramic filter circuits.
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
This amplifier for audio transmission lines was found in a 1961 American publication. The critical...
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...