Found in documentation from the 1980s, this circuit uses an operational amplifier from that time. Transistors are also from the era, and general-purpose equivalents can now be used.
The transistor can be the BD135 and this circuit, found in a 1978 publication, can be powered by...
This interesting circuit measures the distortion of the sinusoidal voltage of the power grid. We...
This sophisticated circuit is from a 1975 documentation. The components are from the time and the...