Well it sounds like you know what your doing to see if you armature is good here is a method that will tell you if its good or bad
Lot of words here but its easy and simple as you will see if you try it
As a note when testing only apply a only few volts.
Remove brushplate hook up 2 wires to transformer only apply low voltage then put 1 lead on commutator segement with other wire touch the segment next to it . If it sparks or armature jumps your good do this until you tested all the segments.
Then touch the armature shaft coming out of it with 1 lead and other lead touch a segment there should be no spark do this with all 3 segments.
Now if the above 2 procedures test ok your armature is good .
