This circuit is an alternative version of the previous one also found in the July 1995 Electronics Now magazine. The triac 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...