Well I've not seen this type before, in a PV studio pro of 1988.
2 springs and 2 coil frames but only one sping per frame. So on diagonal
ends a frame and on the opposing diagonal a taught wire link connecting
the "dead" end of each spring.
Obviously less mechanical power throughput compared to 2 or 3 coils per
frame, offset with more electronic gain presumably. So change of tonal
structure? more bass component equivalent to a tank of twice the length?
or a longer reverb time? or both?