This continuity test was found in a 90s Popular Electronics. The circuit applies a voltage of 300 mV to the component or circuit under test.
Found in a 1965 Radio Shack documentation this oscillator can be used with modern general purpose...
In the figure we have the way to use a single control voltage to act on two varicaps...
Found in a 90s documentation, this switch that is also sensitive enough to operate capacitively uses...