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.

Infrared detector (CB7110E)
Suggested by Mullard in an old documentation, this circuit is based on a common phototransistor and on...
Comparator with Hysteresis LM158 (CB4480E)
Other series operationals such as the LM258, LM358 and LM2904 can be used on this circuit of the...
Differentiator (CB7972E)
This configuration appears elsewhere on this site. This is from a 90’s Popular Electronics and is valid for...