This circuit is from a Popular Electronics from the 90's. The audio amplifier admits equivalent. The others integrated are not very common today.
The filter shown in the figure, suggested by Motorola, operates at a cut-off frequency of 1 kHz,...
This 1965 Philips circuit uses transistors from the era. Modern equivalent components can be used....
This circuit outputs a signal modulated by a unijunction oscillator. The circuit is from a Radio...