This circuit was found in a 1992 publication. What it does is to light an external lamp when it gets dark. The trigger point adjustment is made in a potentiometer or trimpot and the sensor is a common LDR.
The purpose of this circuit, found in a documentation for radio amateurs in 1974, is to amplify noise...
This circuit was obtained in an old American documentation. The integrated circuit used is...
This is a Japanese commercial radio from the 60s. The circuit is listened to by phone and is...