Back to the Hoovers-the Model "O" cutaway looks like someone converted a paddle squirrel cage fan into a vacuum-by putting a bag on the fan discharge and extending the motor-fan shaft to hold the roller brush pulley.Looks like the motor is an induction type instead of universal as on other vacuums.Don't see brushes or brushholders.Would also figure the machine could only be used on AC power due to the induction type motor-at least so it appears.And in those days BOTH types of power were available-power standards haden't been adopted.