This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a high impedance crystal or magnetic earpiece and D1 can be any germanium diode.
This control panel allows the use of NO and NC sensors, turning the alarm on after 30 seconds...
This circuit, found in a 1989 publication, only works with incandescent lamps. The maximum power...
We found this circuit in a 1968 Electronics World. The potentiometer should be set to trigger the SCR...