Found in Electronics now from the 90s, this circuit uses a sensor from the time, which is difficult to find today. The circuit activates a sonalert-type buzzer.
This traditional doubler configuration with the 555 IC can be found in other articles on the...
This circuit is from an 80's component manual. The components are from the time, but the circuit...
This circuit for the 3.5 MHz band (80 meters) was found in an old radio amateur documentation. The circuit...