This circuit activates a buzzer when the voltage applied to the input falls below a preset value in R1. The circuit is from an 80's American documentation.
This circuit was found in General Electric documentation from 1964. It makes use of a PUT, called the...
This mid-frequency amplifier circuit was found in an American publication from the 1950's. The...
The circuit with a common operational amplifier uses a zener as a reference. The circuit is from...