Solid-state variation
     This brings up an interesting thought: what if this addition of a constant current source trick were applied to an existing solid-state amplifier?
    It is an old trick to add pull-down resistors to IC Op-Amp outputs, which forces the Op-Amp's normally Class-B output stage to work in Class-A by drawing extra current through its top transistor and thus improving its sonic characteristics. Why not do the same to a power amplifier? Of course, adding a resistor from output to the negative rail would not be the best approach, as the resistor would not draw a constant current.

    A solid-state constant current source could easily be made that would load down the top output transistors or MOSFETs within the amplifier. This extra current draw would have to be matched by the amplifier's top output devices and it would also force the amplifier to cutoff the conduction of its bottom devices as it shifts its driver's DC output voltage higher to increase the top devices' conduction. So in essence, what  we have created a Class-A-SE/Class-AB-PP amplifier out of an existing Class-AB amplifier.     
   This would make the ultimate accessory for our solid-state brethren, as it would force the amplifier to work in single-ended Class-A mode up to 4 watts of output, after which the amplifier would return to push-pull operation. The additional circuitry (including its own power supply) could be housed on its own chassis.

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