This nice function generator circuit with the XR2206 was found in the May 1977 Radio Electronics magazine. The circuit has a transistor output stage.
This circuit was obtained from an American 80's documentation. The balanced mixer can be shown in...
This circuit was found in a 90s Electronic Engineering. The quadruple operational amplifier can be...
I found this circuit in an English publication from 1989. This configuration can be mounted with...