After the first type Fb 3/5 three-phase locomotives, two more were delivered that did not have carrying axles. The aim was to use the entire weight of the locomotive as adhesive weight, and the locomotives were still capable of a top speed of 75 km/h. This was possible because the outer axles were designed as Klien-Lindner hollow axles. The power was provided by two traction motors arranged low in the frame via jackshafts and coupling rods. 

Thanks to new traction motors, an hourly output of 850 hp could now be accessed per motor. In addition, the pole-changing now allowed four continuous driving speeds of 28, 37, 56 and 74 km/h. Since the traction motors were independent of each other, if one motor failed, the second could still to be used. Since the technology proved so successful, two more locomotives were built in 1919. They were used until 1930, when three-phase operation was ended.