This circuit is from the 1968 ARLL documentation. The MOSFET admits equivalent and the coil determines the operating frequency range being the plug type.
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...