This circuit is from an American documentation from the 90s. The transistors are of power and must be equipped with good heat sinks as well as the integrated voltage regulator.
This filter, which rejects frequencies around 1 kHz, was found in the August 1993 Electronics Now...
This is a voltage regulator circuit for currents up to 1.5 A with an output voltage adjustment for outputs...
This circuit uses an operational amplifier that is still common today. The indication is made by...