Alternatively, the Class-A pairing and the Class-B pairing could share the same type of tube. Two approaches immediately come to mind: give the output pairings dissimilar drive voltages or halve the Class-A pairing's transconductance. The first approach requires as little as using two plate resistors in series. In the circuit shown below, we see differentially arranged triodes with series plate resistors. The bottommost set of outputs go to the Class-B pairing and the topmost outputs go to the Class-A pairing. (A further refinement might be to cross-couple outputs and inputs with small capacitors to extend the frequency response.)   

             Class-A bias point and grid swing

             Class-B bias point and grid swing

     Given the same output tubes, Class-A and Class-B push-pull amplifiers require different drive voltage swings, with Class-B needing more than Class-A. In fact, the ratio is just about 2 to 1. In the Class-A amplifier, the output tubes are biased at the midpoint between drawing grid current and being completely turned off. In the Class-B amplifier, on the other hand, the output tubes are biased at the endpoint just above of being completely turned off. Because a Class-B push-pull amplifier's output tubes need twice the input grid swing to bring the grid to the onset of conduction as the tubes would in Class-A operation, a better ordering might be: EL34s for the for the Class-A grouping and EL84s for the Class-B pairing (or 300Bs for the for the Class-A grouping and 6550s for the Class-B pairing). For example, the EL34 would need to see about 30 volts of peak grid voltage swing in Class-A and the EL84 would need to see about 30 volts of peak grid voltage swing in Class-B. 

    Dual outputs for Class-A & Class-B output pairs

    This same multi-tapping of a split-load phase splitter is easy to construct. However, one liability stands out: the PSRR is substantially worse from the plate as from the cathode. This means that the noise that would normally be cancelled out in the push-pull output stage becomes amplified when the power supply noise presented to the output stage's grids is not equal in amplitude and in phase. Even my trick of giving this phase splitter half of the power supply noise to bring the dissimilar PSRRs into alignment fails when multi-tapped, as the midpoint between plate and B+ has 75% of the power supply noise, whereas the midpoint between cathode and ground only contains 25% of power supply noise. In other words,  this phase splitter can be used, only if an extremely well filtered (or regulated) power supply is used.

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