Intercom with telephone (CB7829E)

Old phones with dials can be used in a simple home intercom system, as this circuit from Popular Electronics from the 90's shows.

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Comparator with Hysteresis LM139 (CB4007E)
This circuit, from the 1990 Motorola Dataar Databook, can use any LM139 series comparator. The circuit...
Antenna Switch using Diodes (CB4156E)
We find this circuit in a 1980s documentation for amateur radio. The circuit shows how to switch...
Peak voltmeter (CB7370E)
With this circuit found in a 1965 Electronic Design, it is possible to read a peak voltage of up to...