The model 31H was made specifically for the balanced output of a Hammond “G-G” Console (IE Model B or C).
I believe that this is no different then the model 31A save for some improvements in the amplifier design. It is at this point (1950) that Leslie adopted a suffix letter to designate the manufacturer for which the cabinet was intended. (H for Hammond, W for Wurlitzer, and C for Conn.)
It is interesting to note that unlike later cabinets, this cabinet featured an ELECTRO-dynamic speaker. What this meant is that the 15″ woofer did not have a permanent magnet, like speakers have today, but rather a large coil of wire which acted as an electromagnet. This coil was also wired in such away that is acted as a filter choke for the amplifier’s power supply