This 1980s circuit was found in Motorola documentation. The circuit uses period components that admit of equivalents. Light feedback in a modern version can be done by optical fiber.
This 1965 General Electric circuit uses a "Thyrector" that is a suppressor of the time. The...
This circuit allows you to adjust the balance between channels of a stereo amplifier. The circuit...
With this circuit of a Popular Electronics from the 90's it is possible to test a diode with the...