Transistorized AM radio (CB8392E)

Found in a 1980s amateur radio QST magazine, this is the conventional circuit of a medium-wave radio. Coils and transformers are commercial types.

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Magnetic Alarm (CB16638E)
The sensors in this alarm are reed-switches. In the diagram we have only one, but several can be...
Who is the fast for 4 competitors (CB3859E)
We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors...
VCO With Operational (CB15466E)
The circuit shown in the figure uses two of the four operational amplifiers found on the LM324...