Unbalanced Input
When used in an unbalanced configuration, the Common Cathode amplifier yields a slightly higher gain and much lower input capacitance than an equivalent Grounded Cathode amplifier. In addition, it does not exhibit the Grounded Cathode amplifier's phase reversal at the output and it boasts a lower distortion figure and, if needed, a high impedance feedback input. All in all, a great little circuit is the Common Cathode Amplifier.

In this unbalanced configuration, the circuit functions like a Cathode Follower driving a Grounded Grid Amplifier. The input triode's plate is, in AC terms, grounded at the B+ connection and its grid receives the input signal, while its cathode is connected to the output  triode's cathode and they both share a resistor whose other end is usually connected to a negative power supply.

In the absence of an input signal, both triodes conduct an equal amount of current, which finds a common path in the shared cathode resistor. As the input signal swings positive, the cathode follows; thus making the grid voltage of the second triode even more negative relative to its cathode. This change in grid-to-cathode voltage decreases the current flowing through the second triode and its plate

load resistor, which defines a smaller voltage across the resistor, which, in turn, defines a positive voltage swing at the output, thus no phase inversion.

As the input signal swings negative, the cathode follows; thus making the grid voltage of the second triode less negative relative to its cathode. This change results in increasing the current flowing through the second triode and its plate load resistor, which defines a greater voltage across the resistor, as the plate load resistor is fixed at the B+ voltage at one end, so the other end must move down in voltage to accept the increase in voltage across the resistor; thus we have phase inversion and a ready high impedance feedback port at the second grid.