An ink supply spool for a thermal ink printer includes a central shaft defining a longitudinal axis, a ribbon hub coaxially mounted about the central shaft for rotational movement thereabout and adapted to support a supply of ink transfer ribbon in a coiled configuration, a torsion spring mounted about the central shaft and operatively engageable with the ribbon hub to rotatably bias the ribbon hub to an initial position corresponding to an unstressed condition of the torsion spring in response to movement of the ribbon hub through a predetermined angular sector of rotation in one rotational direction, to thereby maintain a predetermined level of tension on the ink transfer ribbon, a clutch mechanism associated with the ribbon hub to permit the torsion spring to return to the unstressed condition in response to movement of the ribbon hub beyond the predetermined angular sector of rotation, and a support collar mounted about the central shaft adjacent the torsion spring for supporting the torsion spring during movement of the ribbon hub in the one rotational direction.