In use telephone indicator (CB8657E)

Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be used with extensions.

High impedance preamplifier (CB20259E)
This preamplifier appears elsewhere in this section and this version was found in American...
InfoLITHIUM Charger (CB17181E)
This 2000 circuit, found in the documentation of the time, is intended for charging this type of...
Visual metronome (CB21062E)
Based on the well-known LM3909, this LED pulser circuit was found in American documentation from...