The model 31A was made specifically for the balanced output of a Hammond “G-G” Console (IE Model B or C).
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
