We found this circuit in a 1986 documentation. It uses only LEDs, batteries, resistors and the power supply which can consist of 4 batteries or a 9V battery. The basic circuit uses two-color LEDs.
This circuit simulates the effect of an inductance. Equivalent operational amplifiers can be used,...
This amplifier, from an Argentine publication from the 1970s, uses germanium transistors with...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...