This tunable circuit was found in the May 1994 issue of Electronics Now magazine. The circuit has two amplification stages and excellent gain.
This circuit is from a documentation from the 60s. The circuit can be built with transistors like...
Found in a 1966 General Electric documentation, this dimmer should only be used with incandescent...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...