R_Bleed = R_a || [r_p + (mu + 1)R_k]
This value ensures that whatever signal is present in one channel will be reduced by half in the other channel. For example, if the mu equals 20, the rp equals 8k, the cathode resistor equals 1k, and the plate resistor equals 20k, then the bleed resistor must equal 11830 ohms.
    We can expand the sonic width by cross feeding an inverted phase signal from the opposing channel. Injecting one channel's signal into the other channel's cathode will cause the injected signal to be amplified at the plate, but in anti-phase. (Actually, the phase of the injected signal is preserved, but as the grounded-cathode amplifier inverts the signal at its grid, effectively the injected signal is inverted relative to that channel's normal signal.)

         R_Dif = 0
and at the other extreme:
         R_Dif = muR_k
Ideally, potentiometers would not be used, being replaced by rotary switches, which would allow for 0 and infinity to be the extremes. The use of rotary switches would also allow the mid-position (neither narrowing or broadening) to be realized easily, something that would be difficult with potentiometers.

Balance Control: Left and Right
     Extreme range of control is not the object here. The assumption is that the balance is already fairly close and that all that is needed is a fine adjustment; say a total of 3 dB of range in half a dB increments. Several possible topologies present themselves. We can cascade two series or ladder or combination of attenuators, one fine and one coarse. Or we could place an adjustable resistance in series with the normal volume attenuators. Or finally, we could place the balance attenuator after the input stage. The advantage to this last topology lies in the consistent bandwidth and distortion between channels is better preserved, as each input stage will see the same input impedance from the volume control and will see the same amount of voltage swing. 

    Achieving the 50% mark requires that the difference resistor's value be set to permit one channel's output signal to be reduced by half at the opposing channel's plate. Cross feeding 50% of the input signal to the opposing cathode would yield more than 50% at the plate, as the input signal at the grid is being effectively reduced by the cathode degeneration. But as the cathode resistor only sees a fraction of the input signal, cross feeding the whole of this cathode resistor signal will probably not yield us the desired 50% mark.
    (The cross-coupled phase splitter might be the best circuit to work with, as it might allow a greater amount of control.) Thus, the value of difference resistor one extreme is arbitrarily given by:

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