Tube Amp Tuning for the Best Sound with the Bevois Valley

I explain the tradeoffs associated with setting the bias current on a push-pull tube amplifier and demonstrate the crossover distortion that arises at lower bias current settings. I also talk about the merits of different tube and solid state rectifiers. The amplifier under test is the Bevois Valley, designed by Morgan Jones and built on an old Magnavox chassis, the 9300. The amp uses four 6BQ5/EL84 pentode tubes and two 6DJ8/E88CC/ECC88 triode tubes. The version shown on the bench used a 5U4GB rectifier tube, and the final version uses a 5AR4. In between, I tried out a solid state rectifier (i.e., two diodes). I use the original Magnavox power transformer and two Dynaco Z565 output transformers (those originally used on the ST-35).

Finally, I listen to the amplifier play "Make Me Smile" by Chicago and "Tempted" by Squeeze.