Endless loop recorder having temperature compensated tensioning

A data recorder comprising a recording medium in the form of an endless loop of magnetic tape, and magnetic head means, the magnetic tape being wound around former means comprising a plurality of roller members to provide a tape store, the roller members and inner turn of tape in said loop defining within the center of the store an area in which the magnetic head means are mounted, at least one of said roller members being mounted near one end of a movable arm, means mounting said movable arm for pivotal movement in a plane parallel to the plane of the endless loop whereby pivotal motion of the movable arm adjusts the tension in said tape, temperature-sensitive expandable means to pivot said movable arm in accordance with temperature changes, said temperature sensitive means being providing pivotal movement of said movable arm to an extent which compensates for the change in loop length due to the same temperature change so as to maintain tape tension substantially constant.