This circuit is from a 1975 RCA tube manual. It appears elsewhere on the site. R5 depends on the voltage of the amplifier with which it is used and can be changed.
Two operational amplifiers 741 are used in this circuit that must be powered by a symmetrical...
The direction of rotation of the M motor can be controlled by an Arduino or another...
Found in a 1965 Electronic Design, this circuit makes it possible to select signals with an...