The operational amplifier for this tone control found in a 1977 Signetics manual may be the 741. The power supply must be symmetrical and the signal cables short. The bass gain is 20 dB.
This simple unijunction circuit is from a Radio Electronics from July 1963. It can be assembled with a...
Using 555 integrated circuits, this alarm circuit was found in a 90s American documentation. The signal...
This circuit with transistors was found in an old Japanese publication, translation of an American...