For use in a high performance valve compressor/amplifier etc using either an ac coupled single ended or push-pull output stage. Can be used with a secondary load resistor e.g. 200 ohms will provide a constant reflected anode to anode load of 16000 ohms when the amplifier is feeding a high impedance load. This also lowers the effective output impedance of the amplifier and may be adjusted to define the amplifier gain. When used with a push-pull output stage the quiescent dc anode currents must be balanced to within 0.5 mA. Combination core using High grade Grain Oriented Silicon Iron (M6) and Mumetal (76% Nickel). This provides a high level capability, exceptional bandwidth and transient response which is maintained over the full dynamic range. This core also permits the use of a relatively high ratio which ensures minimal loading of the anode and a low output impedance for driving lines or complex loads.