I recently learned a section of the Clavinet part in "Waterfall." This is the verse starting at ~2:18. I included the bass part too, although the rhythm for the last measure or so isn't right.
From what I can tell, Richard Tandy had a Clavinet D6. In this picture dated August 1978, it's visible at the very bottom:
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(For the record: I think the other keyboards here are a Yamaha grand piano [the liner notes for A New World Record specifically list "Yamaha C7 grand piano"], a Yamaha CS-80, a Mellotron M-400, and - easier to see from an-other angle - a Moog Polymoog and a Wurlitzer 200).
From the Clavinet user manual (available here): "The register tabs on the left-hand panel are marked AB, CD and are connected to the sound pick-up for a wide variety of settings. As required, they switch both pick-ups either singly or parallel, whereby the polarity of one of the pick-ups is reversed to cancel overtones or to add them. Thus the AB and CD registers produce tone colours in every position...."
I have a Nord Electro 5, which - as far as I can tell - separates out these AB and CD tabs into four distinct sounds. To try to replicate an authentic sound, I recorded B and then overdubbed D. I'm not sure if that's what Tandy used, but I thought it sounded the closest.
