Abstract: The elongated drum guide (1), on which the two drum-shaped parts of the drum arrangement around which a magnetic tape is guided in one helical turn are held in place, has pairs of seating ribs running circumferentially in a cylinder-arc cavity for seating the two drum parts in the proper alignment and at the proper spacing from each other to allow a head wheel to revolve in the slot between the parts (2, 3) Screws (20) pass through the drum guide (1) and through the seating ribs for holding the drum parts in place in such a way as to provide no strains producing long-term deformation, while at the same time assuring precision of reassembly after demounting the scanning device for replacing the magnet heads of the head wheel. The drum guide is made of a light metal alloy and the seating surfaces of the internal ribs are machined by electric spark erosion to provide the necessary precision and also a hardening of the surface.