This input circuit for an oscilloscope was found in Radio Electronics from the 90s. The operating circuit is from that time, and a modern equivalent can be tried out.
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...