The heat-sink plates on which the rectifier diodes are mounted are fastened to an insulating base member essentially of the shape of an arc of a circle of between 240.degree. and 320.degree.. Opposite the position of each of the diodes, which each have a lead extending alongside but spaced from the insulating member, a connection device with inwardly and outwardly extending lugs is affixed to the insulating base member, the inwardly extending lug being connected to the diode lead and the outwardly extending lug being connected directly (or indirectly through a strapping wire) to a lead of the stator winding of the alternator. This construction enables diode leads to be connected before installation of the rectifier unit in the alternator casing and facilitates soldering the stator winding leads to the assembly. The connectors may be crimped sleeves or bent-up wire devices.