a greater grid-to-cathode voltage than the second triode, which would countervail the greater voltage on its plate. The disadvantage to this approach is that the added resistance might excessively lower the gain of our amplifier. Thus, a better approach could be to use a string of forward biased diodes to shift the DC level of the first triode's cathode more positively than the second triode's, without adding a signal degeneration. The disadvantage to diodes is that the circuit should be built with a negative power supply, as the remaining cathode resistor is now much smaller in value, which could limit the input overload voltage excessively.

  This last disadvantage can be overcome by capacitor coupling the input, which would allow for separate biasing of the grids and the use of a greater valued cathode resistor. In this variation, gain is preserved, current is equally shared between triodes, and noise at the output would be lessened, assuming the values of the resistors at the second triode's grid were chosen carefully. The power supply noise that normally would voltage divide at the output is here diminished because the sampling of power supply noise at the second grid is then amplified and inverted at the plate, which will subtract from the power supply noise present at the plate.

Dissimilar Plate Voltages: Hybrid Circuits
   Before moving into the circuits, we should consider just how a Common Cathode amplifier works. In effect, the amplifier is composed of a Cathode Follower feeding a Grounded Grid amplifier. This explains the high input impedance, the phase preservation, and the high gain of the Common Cathode amplifier. Now, if we treat the circuit as two circuits, we are free to optimize each in different directions.

   Of course if we set the first grid DC voltage to ground level, then we will not need an input capacitor. And if we are willing to forgo the possible noise reductions that derive from connecting the two resistor voltage network to the power supply, we can attach the network to the output and to ground. This arrangement will provide both a little DC and AC feedback to the second grid. If primarily AC feedback is desired, then the resistor values should not be too high, as the second grid sees more input capacitance than the first grid and consequently it is much more sensitive to high input impedances. If solely DC feedback is desired, then the resistor values should be as high as possible and the bottom resistor should be bypassed with a capacitor to shunt away the AC signal.

   For example the Cathode Follower can be based on pentodes just as well as triodes. In fact, as long as the pentode's second grid is well decoupled from the power supply noise, the pentode has the advantage of a better PSRR figure than a comparable triode based Cathode Follower. The Grounded Grid amplifier, on the other hand,  works best with a triode. Combining both tube types can be achieved by using duo tubes such as the 6AN8,