Taken from a 1967 RCA publication, this circuit maintains a low current in the battery when it is charged. The components are from the era.
This filter was found on a 90's Radio Electronics. With the components used the cutoff frequency...
This circuit is from an American publication of the 80's. It makes use of components of the time....
This circuit was found in a 1992 PE Hobbyst. The circuit detects the presence of spy...