A power transformer apparatus and method of assembling are provided. In one aspect, a method of assembling a transformer is provided. The method includes providing a heat sink including a plurality of exterior ribs, wherein the heat sink forms a bottom wall of an enclosure. The method also includes coupling at least one diaphragm to the heat sink such that a bottom surface of the diaphragm is in contact with the heat sink, coupling at least one winding to the at least one diaphragm, and coupling a terminal board to the heat sink such that a plurality of spacers are positioned between the terminal board and the heat sink.