The circuit presented is a Japanese commercial radio from the 1960s. With a 4.5 V supply, it is a super-heterodyne type with an IF of 455 kHz. 6 germanium transistors are used.
This circuit is from a Popular Electronics from the 90s. The integrated circuit admits equivalents...
This very interesting project was obtained in a 1980 publication. It consists of a device that is...
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...