This circuit is from a Radio Electronics from August 1992. The transistor used allows the control of motors up to about 5 A. It must be equipped with a heat sink.
This instrumentation amplifier with differential inputs was found in documentation from the 90s....
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
Found in a 90s 303 Circuits, this circuit has an output power of 100 mW. L1 consists of 890 turns...