I need to find the pic I have of this whole unit. This was an odd piece of equipment - a MECHANICAL rectifier unit. It used a synchronous motor to rotate a spindle having four metal rods, then above and below each rod was a metal shoe, and at the correct time of the AC power cycle, the rod would be positioned to arc from one of the top shoes across to one of the bottom shoes. The top shoes were fed from a large transformer in the bottom of the unit (about the side of 2 fridges side by side) - they were connected as L1 - L2 - L1 - L2. The two bottom pairs of shoes was where the high-voltage DC was derived and you can see the left pair for the negative side and the right for the positive. Can't imagine that the output was very 'clean', but this apparently powered an early X-ray machine.