For low-frequency signals, this circuit transforms a single oscilloscope into a dual-trace. The circuit is from Radio Electronics magazine, October 1984.
This small general-purpose mixer uses only two transistors. We found it in a Radio Electronics issue from...
This full wave switch using SCR for the power grid is one of many versions we have on the site....
The operational amplifier of this balanced circuit is old and can, however, be implemented with...