A high voltage transformer (50) includes a magnetic core (5); a low voltage winding (10); a high voltage winding (20); at least one inner sleeve (30); and a coil bobbin (24) for carrying the high voltage winding (20). The coil bobbin (24) is configured to be arranged inside the at least one inner sleeve (30) and configured to be attached to the at least one inner sleeve (30) at an outer perimeter of the at least one inner sleeve (30). The coil bobbin (24) includes at least one field-control electrode (22), which is adapted to shape an electric field generated by the high voltage winding (20).