I hope this helps answer questions about the AC to DC Mills (Sandell)
rotary converter:

1. The AC side has large terminals on the end of the unit facing
outwards (sideways).  I believe these contain the brushes for the
AC side slip rings.

2. The DC side has the segmented commutator with 4 rectangular
brushes.  You can see these from the outside of the unit.  This (DC)
side has the smaller terminals are on the top of the unit, and face
upwards.  (Usually, if looking at the nameplate, the AC side is on the
left).

3. My converter is 2.5 amp, and is in my single Violano.  I don't
think it was ever changed.  The mounting holes are original.

4. The polarity, as Mike Ames noted, is random.  This will not matter
in a Violano.  It works with either polarity.  Some say that the random
polarity keeps anything from being permanently magnetized; I don't
believe this to be significant as I have, in addition to my converter,
a power supply I built with a fixed output polarity which I use most
of the time.  I have no ill effects of permanent magnetism.

5. There is a significant shock hazard when the converter is installed
in a Violano.  There is a splice inside the conduit of the Violano that
connects one leg of the AC and DC sides of the converter together.  So,
depending on which way the AC plug is inserted in the wall socket, you
have a 50% chance of the metal parts being hot relative to ground (water
pipes, heating ducts, electrical wall plates, wet concrete floors, etc).
Do not work on a Violano anywhere near a ground if using an original
converter with the original conduit wiring.

I hope this helps.

Dick Hack