The Williamson design demonstrates the maturity that tube amplification had reached by the late 1940s. Other than the British Mullard 5-10 circuit and David Hafler's Dynaco ST-70, there was little improvement in the fundamentals. One improvement that was widely used was an output transformer with additional taps allowing use of Blumlein's distributed load or ultra-linear technique, which allowed the output stage, before applying feedback, to operate at a power intermediate between that available from a triode and the significantly higher power from a pentode or beam tetrode, with distortion better than either.