Indicated for automotive use, this circuit was found in a Popular Electronics from the 90s. The circuit uses a power transistor that must be equipped with a heatsink.
This circuit can decode an audio tone whose frequency depends on R1 and C1. R1 can be in the range...
This is the basic configuration of an operational amplifier amplifying signals from a photo diode....
This regenerative circuit was found in a Japanese publication from the 1960s. Details of the coils...