This circuit automatically turns off small battery-powered devices after a certain amount of time, saving battery life. We found it in a Popular Electronics from the 90s.
This transmitter for the 80-meter band (3.5 MHz) was found in an old documentation for radio...
This interesting bandpass filter using an operational amplifier 741 has its cutoff frequency...
Found in 1966 General Electric documentation, this circuit uses solicon unilateral switches (SUS)...