Pure Class-A
Push-Pull Distortion Cancellation
      To those who queried the need for complementary inverse pre-distortion to lower the distortion of a push-pull output stage, you intuition is sound, as the inverse pre-distortion technique is definitely better suited to single-ended gain stages. The Class-A push-pull output stage already intrinsically cancels much of its output devices' non-linearity. The push-pull output stage (run under Class-A operation) effectively adds the two output devices' non-linear transfers into one flatter transfer function.

    The composite curve are made by subtracting the second output tube's current conduction form the first. At idle, when bottom tubes conduct equally, the two currents equal and thus cancel, which places the center of the composite curves at zero grid volts and zero current into the load. As the output stage is driven by inverted drive signals, the non-linear transfer curves are averaged. So one tube's greater conduction is met with the other tube's lesser conduction, hence the straight lines formed in the composite plate curves drawn from two output tubes operating in pure Class-A and the wobbly curves formed by the same tubes in Class-AB. 

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