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6. The Power Amplifier > Single-Ended Madness - Pg. 480

480 Valve Amplifiers Although substituting one stage that combines the functions of input, phase splitter and driver does not achieve the linearity of purpose designed stages, it achieves better linearity than the Mullard circuit because less gain is demanded from it. With only a simple driver circuit and output stage within the global feed- back loop, the elegant Quad II has no stability problems, but it has by far the smallest output transformer of all three amplifiers. A small output transformer always means compromised primary inductance, which means that much of the output stage's available current is wasted driving the output transformer's reactance rather than the external load. However, remember that the Quad II was designed to drive an electrostatic loudspeaker (open circuit at low fre- quencies), so this weakness was not apparent in its intended use. NEW DESIGNS We have investigated individual stages, we have looked at functional blocks, and we have seen how classic designs were configured. Rather than merely observing, it is now time to put that knowledge to use, and design an amplifier. In early editions of this book, it was suggested that an old amplifier could be cannibalised for its transformers and chassis. Sadly, this approach can no longer be justified because classic amplifiers are now likely to be fifty years