This receiver uses old transistors that are equivalent to BC548 and BC558. The photo diode is of any type. The receiver can be used on a highly sensitive audio link.
This well-designed sinusoidal oscillator by Wien bridge was found in ancient European...
This is a circuit for testing small lamps and LEDs. The lamps that can be tested are the ones...
Found in a Popular Electronics from the 90's, this circuit can be implemented with almost any...