A field deflection amplifier (21) generates a field deflection current in a field deflection winding (Lv). An LC resonant circuit (22) is coupled to the deflection winding (Lv) and to an output switching amplifier (Q4). A control circuit (26) switches conductive states of the amplifier (21) at a line rate, with a 50% duty cycle, to excite the LC resonant circuit (22) into providing a line rate correction current for the field deflection winding (Lv). The control circuit (26) varies the modulation envelope of the field deflection current at a field rate in a generally sawtooth manner to provide north-south pincushion correction. When used in conjunction with raster scanning in a square-planar picture tube (SP), the modulation envelope is nonlinearly waveshaped to take into account the aspherical nature of the picture tube faceplate.