This circuit was obtained from Dutch documentation from 1967. It uses transistors of the time which can be the BFY50 and 51 for the output and the BC series for the others.
This circuit was obtained in an American documentation translated in the 80's. The circuit can be...
This circuit is from a 1998 Electronics Now and can be easily assembled since it uses a common...
This circuit was suggested by National Semiconductor in its Linear Application Handbook. The...