Abstract: A welding apparatus is disclosed to include an electrically insulating casing, first and second welding electrodes, and a welding transformer having a toroidal core, a multi-turn primary winding and a single-turn secondary winding. The core includes a grain-oriented silicon steel material coiled with an insulator. The primary winding has turns axially wound about the core. The secondary winding includes two conductive arm sections which are connected to the electrodes and a wound section including conductive wire cable which electrically connects the two arm sections. One of the arm sections can provide the frame member to support the transformer. The apparatus is suitable for spot or linear welding.