The Sample & Hold is another dual module in the Synthasystem. While it doesn't have a built-in clock (it requires external triggers), each S&H circuit has its own random voltage generator, which is a nice feature. Any external source can also be used.
As you can see, this uses the rather rare 2N4891 UJTs ($10 for each of those tiny metal cans!!), though some other UJTs may work. Take note, too, that good quality caps are needed here - I've used styrene.
Since I'm using banana jacks, this module becomes a bit more complicated. The unit is designed for switching jacks on the signal inputs: when no plug is inserted, the input is the internal noise generator. I'll just be adding a couple switches to the panel to take care of it. Besides the switches, signal input, trigger input, and output, each S&H unit also has an output level pot.