Telephone Busy Indicator (CB24430E)

This circuit for analog telephones from the 90s was found in documentation from the time. It lights up a remote LED when the extension is in use.

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Capacitance Multiplier (CB6228E)
We found this circuit in an old Signetics documentation. The integrated circuit is of the time,...
Octave equalizer (CB7978E)
Found in Precision Monolithics documentation from the 90's, this circuit equalizes octave signals...
Triangle to sinusoidal converter XR2208 (CB24549E)
This circuit for frequencies up to a few tens of megahertz was found in the April 1978 issue of...