Abstract: An amplifier circuit for amplifying a repetitive alternating signal, the amplifier circuit having a voltage feedback loop which includes a sampling circuit. The sampling circuit is arranged to sample the output voltage of the amplifier at a given time during each cycle of the alternating signal and to store the sampled voltage for the remainder of the cycle. This stored voltage is used as a feedback signal for the amplifier. Since the output is sampled at the same time during each cycle of the alternating signal the filter circuit in the feedback loop may be omitted and the phase shift introduced by the feedback loop may be arranged to be constant with varying frequencies. When used in a field deflection circuit for television display apparatus the deflection waveform is preferably sampled during the flyback period.