I have built a Tubular Cluster Array from Stan's drawing, with four 3" tubes.
I have built a power source, consisting of a Variac, Diode Bridge, fuses, a 1/2 horse power motor @ 1725 rpm, pulley a bit greater than 2:1, and a de-regulated Delco Remy Alternator.
It is not finished, but it runs.
First Run (last night)
Tap Water
0-5 psi in about a minute, max on my gauge
Lots of scum, deposits and cloudy water
Up to 30 volts on the Variac, then blew a 5 amp fuse
Second Run (today)
Distilled Water
0-1 psi in a few minutes, extremely reduced production
No scum, no deposits, clear water
Up to ~50 Volts on the Variac, then blew 7.5 amp fuse
Motor can handle it
Alternator gets hot
Cell stays cool
Pretty much as you see in these diagrams.