The 4712 Reverb module was the second module I did for the 4700 series synthesizer. I had built 2 modules similar to this into my big homebrew Paia rig I had built before I worked for Paia. John liked how it rounded out the clinical sound of the modules, so he immediately wanted me to add a similar module to the 4700 lineup.
My original design was based on the OC Electronics folded line reverb tank, which is all I would ever use when modding guitar amps and such during my Headway years. Their folded line reverbs are the only thing out there that sound realistic, and avoid the "springiness" of standard tanks. But, cost won out and Paia used Accutronics tanks instead. OC was a very small operation up in Wisconsin, and all the reverb units were hand made, so the tanks were more expensive, and John was all about cost reduction.
Owners Manual here - a pretty bad bitmap scan from around the web somewhere