Abstract: A heat sink (50), on which is mounted heat producing elements, such as transistors (40-43), is contained entirely within a cabinet (10) provided with openings (20, 27) positioned directly below and above the heat sink. The heat sink includes a rectangular plate (52) with the transistors mounted on one side and a plurality of integrally formed parallel fins (60) projecting laterally from the plate on the other side and extending diagonally thereacross. The heat sink may be convection cooled by air entering the openings (22) in the bottom of the cabinet and exiting through openings (27) in the top, or the heat sink may be forced air cooled by means of a fan (75) mounted the rear panel (16) which draws air through the openings (22) and across the fins (60).