This 6-transistor radio was sold in Japan in the 1960s. The super-heterodyne circuit for the OM band was powered by ordinary batteries.
This circuit is from a 1995 Electronics Now. It generates a 1 kHz sinusoidal signal. See in the...
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....
This circuit was found in an English documentation from the 90's. The circuit has the frequencies...