Found in Precision Monolithics documentation from the 90's, this circuit equalizes octave signals determined by the capacitor values according to the table next to the diagram.
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...