Here is a perfect replacement for your North Electric ringer, North Electric used the worst ringers there are. They never rang well from the beginning. When you find these phones either they have a party line ringer or a dead ringer. The Galion or 7H6 and some subsets or ringer boxes had these ringers. Here is the best replacement. 

We have found that the Leich armature fits perfect in these phones with out modification.

You keep the mounted North bells in place and mount our Leich armature and now you have a great working ringer.