[sdiy] Little help with S and H circuit

[prophecysound]

Hey all.....

I'm struggling to get working a S&H circuit that is mostly based on one 
of Tom G's early LFOs:
http://prophecysound.com/temphost/sandhschematic.pdf
(Adobe v6 required)
I lack the understanding to debug the CA3080 control part - what I have 
is that there is +/- approx 12V waveform at L2 (I'm running this from a 
+/-15V power supply) but I'm not getting a changing CV at the output ... 
a few questions:
1) what is the purpose of the C3/R12/C5/D1 components?
2) should the collector of Q1 be unconnected or connected to ground? 
What purpose does C1 serve?
Oh, and I'm using a 2N5484 instead of the MPF102 - I guess I might need 
to tweak the circuit to allow for a different switching voltage but I 
don't think that's the trouble for now, I think the CA3080 switching 
part isn't working.

Any hints or tips GREATLY appreciated. I can provide more diagnostic 
voltages if need be.

Cheers

MikeB