This wired intercom circuit was found in an English publication from the 80's. The integrated circuit can be replaced by an equivalent, just like the transistor which is a general-purpose type.
This is the circuit that decodes the signals from the CIR3059. The adjustment of each frequency is made in...
This circuit measures the strength of audio signals. We found it in an American publication from...
This circuit is from a 1974 Ferranti transistor manual. The circuit is analog, and the components used...