Quoted from Shiny_balls:On PBR website, there are 2 different type of armatures with insulated arms..........A.C. and D.C.
I know mine is an EM but......umm I'm really not sure .....I have heard some D.C. on final EM machines....
It looks like the only difference between the AC and DC armatures is the addition of a washer on the DC one. Not sure what/where these washers are, but maybe you can check the ones currently on your machine?