This circuit that imitates the sound of the cowboys' calls with their “louder” was found in a Hands On Electronics from the 80's. The integrated circuits used are from that time.
This 1987 signal injector included the power supply from the power grid. The transformer is 6 + 6...
This amplifier was found in a 70s documentation. The product gain x bandwidth is 350 MHz. The...
This simple receiver with junction FET uses a high impedance magnetic earphone (over 2 k). Power...