This circuit is from an American documentation from 1975. The circuit uses components of the time which can be replaced by modern equivalents. The coupler is homemade with a lamp and a photocell.
This old oscillator using germanium transistors has a high impedance headphone as inductor to...
This circuit from a Popular Electronics from the 90's can generate signals from 0.03 Hz to 3 kHz...
This is the traditional configuration of an unregulated bridge rectified power source. The circuit...