Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
This circuit is from a Radio Electronics magazine from August 1960. It is a commercial circuit for marine...
The Texas Instruments LM5178 Buck-boost controller is capable of operating in the 4.2 to 55 V (60...
This is a typical 80's FM radio mixer circuit. The circuit was found in a documentation of the...