We found this circuit in an old RCA publication. The components are of the time, admitting equivalents. The circuit is triggered in two ways using LDRs.
We found this receiver for medium and short waves in a publication from the 1980s. The medium wave...
Found in a 90s Radio Electrconics, this circuit is an operational one with a power stage using two...
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...