For example, when the plate load equals the r_p of the triode, its transconductance is halved, as G_m is equal to mu / (r_p +R_a). Adding an unbypassed resistance in series with the cathode also decreases the triode's transconductance. When the cathode sees a resistance equal to r_p / (mu + 1), the effective transconductance is halved. For a 300B, this resistance would equal 143 ohms. Notice that resistance is too low to correctly bias the 300B. Thus slight modification is required and is shown below.

          Split-load phase splitter with multi-taps

     Cathode bias with transconductance halving

     The problem with cathode bias is that while it works beautifully with Class-A amplifiers, whether they be single-ended or push-pull, it does not work well with Class-B amplifiers. The reason is easy to discern: in the Class-A amplifier the idle current is equal to the average current through the output tube even when the amplifier is putting out its full output. In contrast, the Class-B amplifier's idle current is but a small fraction of its conduction at full output, making its average conduction roughly half of its peak. In other words,  cathode bias would results in the Class-B amplifier trying to turn its self off during heavy use, creating a good amount of distortion in the process.
     The solution is to use only fixed bias for the Class-B pairing.

Split-load phase splitter's PSRR per tap when fed an input signal with 50% of power supply noise

     The other approach is to give all output tubes the same drive signal, but halve the Class-A pairing's transconductance, which would require an effective doubling of its drive requirements. How can a triode's transconductance be decreased? Well, just placing a plate resistor in series with the triode will reduce its transconductance, as a triode is sensitive to its plate voltage, which this resistor will alter.

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