A guide drum comprises a stationary drum having a tape guide for guiding a magnetic tape along a predetermined tape path and a rotary drum rotatably provided with respect to the stationary drum. The rotary drum has at least one magnetic head for recording and/or reproducing a signal on and/or from the magnetic tape which is wrapped spirally around an outer peripheral surface of the guide drum over a predetermined angular range. The guide drum comprises first and second tapered parts which are formed with reference to a reference position having a specific height from a lower edge of the rotary drum. A diameter of an outer peripheral surface of the first tapered part gradually decreases toward the stationary drum, and a diameter of an outer peripheral surface of the second tapered part gradually decreases in a direction away from the stationary drum.

Improvement of a lower cylinder of a drum assembly for a helical scan type magnetic recording/reproducing apparatus, a magnetic tape being wrapped around the drum assembly in a predetermined angular range with respect to its own axis which is wider than a scanning angular range so as to have an additional tape-wrapping angular range on at least a tape-entry portion from which the tape starts to be wrapped around the drum assembly. The lower cylinder integrally has on its outer circumferential surface a tape-guiding portion for guiding the tape on wrapping it around the drum assembly, a tape-wrapping portion on which the magentic tape is wrapped along the tape-guiding portion in a direction substantially coincident with a direction of rotation of the upper cylinder and a protruding portion formed in the additional tape-wrapping angular range so as to be protruded by a predetermined amount with respect to the tape-wrapping portion. The protruding portion initially comes into contact with the tape to be entered onto the drum assembly and has a wedge-like shape in which its top is substantially directed in the tape-travelling direction. The protruding amount of the protruding portion with respect to the tape-wrapping portion being substantially equal to a protruding amount of the magnetic head from an upper cylinder of the drum assembly.

A tape guide device of a rotary head type video tape recorder of the helical scanning system including a shoulder portion formed on an outer circumferential surface of a lower stationary cylindrical portion cooperating with an upper rotary cylindrical portion and constituting a head cylindrical drum for guiding a magnetic tape. The shoulder portion has, in a section thereof with which the magnetic tape is not brought into contact, a configuration consisting of a plurality of parabolic lines connected to one another. Alternatively, the offset portion may have a configuration consisting of curves which are such that their second differential coordinates are continuous over the entire circumference of the head cylindrical drum with respect to the fixed coordinate system disposed on the outer circumferential surface of the head cylindrical drum, or the shoulder portion may have a configuration consisting of curves which are such that the absolute value of the maximum value of the second differential coefficients is not equal to the absolute value of the minimum value thereof.

A magnetic head drum includes an upper section that carries a set of magnetic heads and rotates at a preselected head speed, and a stationary lower section that is characterized by a reduced diameter step formed along the tape wrap path thereover (e.g., a helical path for a helical scan recorder). Because of the reduced diameter step, tape pressure is shifted from the lower drum section to the upper drum section which, by virtue of its rotation, produces a low friction air bearing. The reduction in diameter to produce the above-described step, moreover, results in a shoulder or ledge along the lower edge of the tape wrap path, which shoulder serves as a guide for the tape, and promotes accurate tape tracking over the drum. The amount of reduction in diameter for the lower drum section is not chosen arbitrarily, but is preferably within a range of 1 to 6 mils. In this range, a desirable balance is achieved between reduction in frictional drag and limiting of forces tending to distort the tape. Moreover, it appears that a reduction greater than around 6 mils tends to result in increased tape flutter.