This balance indicator for stereo amplifiers was found in an 80's Elektor. The components used are common. Zeners are 1.8 V or close to that value.
This circuit allows you to modify the resolution of a measurement bridge. It was found in the...
In the figure we have a three-phase AC motor control for voltages up to 600 V or 1200 V depending on...
This small experimental transmitter with the CK722 transistors was found in Radio Electronics...