Synth-Diy archive, S&H question

[--M]

    Hey all I had some questions about sample and hold and thought I may
be able to find some answers in the synth-DIY archive but I can't seem
to find it.  Any pointers?

    Specifically I was looking at Tom's LFO5a, it has what appears to be
a very simple S & H circuit built from 2 J-fets, but I don't know why
and how it works.  What sort of signal does the S&H *in* expect?  In
commercial synths with hardwired signals, what do they feed the S&H in?
How is the randomness generated?  That is, I see the clock *in*
selecting what point on the incoming wave to sample from, but if you
feed it a triangle wave, say, then wouldn't it just be a stepped
triangle at the output?