This bidirectional circuit was found in an American documentation from the 80's. The LEDs are common red, and the resistor is calculated according to the formulas next to the diagram.
Found in an old publication, this is a transmitter with a spark coil. The high frequency...
This circuit was found in a 90s Hands-On Electronics. When a signal appears at the headphone...
In the figure we give a suggestion of a high-power stage to excite a speaker with the 2N3055. The...