This circuit was found in a National Semiconductor Handbook from the 1990s. The integrated circuit used is from the time and the circuit is stereo.
A circuit for controlling the temperature of a heating element was found in a Mullard transistor manual...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...