Sensitivity control for phototransistor (CB8081E)

This method of controlling the sensitivity of a phototransistor was found in an Electronics Now from the 90s. It applies to any phototransistor.

Three-phase motor control (CB7268E)
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....
FET Switch (CB6725E)
This switched filter was found in the 1969 documentation. The FET should be current-matched and eventually...
Double LED CMOS Flasher (CB5206E)
The frequency of the blinking of this circuit is given by the capacitor that can have its value...