Dynamic compressor (CB21762E)

This circuit was found in a 1977 publication for radio amateurs. Transistors are common general-purpose types of the time.

Shutdown for exhausted battery (CB8387S)
When the 24 V battery voltage drops below 18 V, this circuit cuts off its discharge. The circuit...
Binary counter with relays (CB23779E)
This circuit uses the flip-flops from the previous circuit to implement a 3-digit binary counter. The...
Magnetic Transducer Detector (CB15914E)
This circuit, suggested by Philips Components, uses as a base a voltage comparator of the type...