When the 24 V battery voltage drops below 18 V, this circuit cuts off its discharge. The circuit is from 1968 documentation. It can be adapted to operate with other voltages.
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...