This circuit was obtained in an American documentation from the 80's. The transistors can be equivalent to those indicated and the crystal can reach a few tens of megahertz.
This instrumentation amplifier with differential inputs was found in documentation from the 90s....
This signal follower was found in a 1976 publication. The FET can be BF245 or MPF102 and any...
This is a simple circuit to control a set of lamps from 3 different points. We found it in an old...