Ya' know what? Even Model T generators had a movable third brush plate. But it was a little more complicated to set up the third brush plate initially in a Model T generator. Once set up, however, moving the third brush plate like a Model A adjusted the charging rate. You first had to loosen a nut inside, though. Move the plate in the same direction as in a Model A generator, find the rate you like and then tighten the nut back up. Yup! Henry made it easier in his Model A!
Marshall