We found this circuit in a 1991 Hobbyst Electronics. The circuit makes use of an unusual transducer today. It is a piezoelectric buzzer that can eventually be replaced by an equivalent configuration.
This typical crystal oscillator configuration can generate signals up to a few tens of megahertz...
This simple servo can be built by coupling a potentiometer to a reduction box with a 3 to 6V...
This constant current source for high voltage loads was obtained from a 1967 General Electric...