A high voltage horizontal flyback transformer assembly includes a generally rectangular ferromagnetic core with a pair of opposing core legs. A primary or low voltage winding is split into two portions each mounted on a different core leg with the winding distributed so as to cover as much of the core as possible. A high voltage winding is split into two or more portions, each placed as close to the core as possible and each wound in such a fashion as to cover as much of the core as possible, to thus increase mutual coupling. In particular, one half of the total high voltage winding is concentrically mounted over each of the low voltage portions. One or more diodes are located in series between the high voltage portions to reduce the effect of the high secondary distributed capacitance on the primary circuit, equalize the ringing frequencies of each high voltage section, and provide high voltage rectification. The entire transformer assembly, including the diodes and a focus resistor, is mounted in an oil-filled container.