One rationale for linear arms was to maintain perfect tangency to the groove, following the track of the cutting head across the lacquer. In comparison, pivoted arms are truly tangent at only certain radii on the record, and this can result in distortion.
Linear tracking arms are far from simple in operation. TWL mentioned air bearing versions with pumps, and there have been others with multiple rotating rods or servo motors to facilitate the arms' lateral mobility, especially as required to track off-center records.
Linear tracking arms are far from simple in operation. TWL mentioned air bearing versions with pumps, and there have been others with multiple rotating rods or servo motors to facilitate the arms' lateral mobility, especially as required to track off-center records.