This circuit of the 70's uses transistors of the time. The circuit can amplify signals from 10 Hz to 100 kHz and modern equivalent components can be used. The circuit is from Ferranti.
This circuit from an old Argentine publication shows how it is possible to use a tunnel diode in a...
To invert the rotation of a motor by changing the levels of an Arduino output or another...
This ultra-low distortion driver was found in 80's Analog Devices documentation. The circuit has a...