Abstract: A thin wall, stainless steel transformer case of rectangular box configuration is comprised of edge welded steel plates with its sidewalls and end walls bearing vertical, U-shaped bonded channel members of copper for mechanical reinforcement of the case and for forming transformer heat dissipating fins. Stainless steel reinforcing channel members are similarly bonded to the outside of the case bottom wall and the cover. An epoxy fiberglass strap spanning interiorly between the sidewalls of the case at its upper end and bolted to opposed brackets press the transformer core against the bottom wall of the transformer case. A pair of deformable tubes sealably project through the cover for effecting vacuum evacuation of the interior with the cover sealed to the case and for feeding insulating dielectric liquid to the transformer case interior. The tubes are pinched off and sealed after filling.