meeting all the previous design objectives, it would match last month's phono stage nicely. Once again: the CCDGC amplifier consists of a Grounded Cathode amplifier directly cascaded into a Cathode Follower. Each triode sees the same cathode to plate voltage and the same load resistance and current draw. Both are in voltage phase, but not current phase. (As the grounded Cathode amplifier sees a positive going input signal, its plate current increases, which increases the voltage developed across the plate resistor, which in turn swings the plate voltage down. This downward swing is then cascaded into the grid of the Cathode Follower, which decreases the plate current to the same degree that the previous stage's current increased.) This results in the constant current draw feature of this topology (a highly desirable feature, as the signal amplification will not alter the amount of current being sourced from the power supply and consequently not perturb the power supply, thus greatly simplifying the design consideration of the power supply)."

"The type of circuit used to obtain complementary distortion cancellation is shown in Fig. 1. A simple voltage amplifier is followed by a cathode follower. It is very convenient to use a connection of this sort because of the common availability of two triodes in a single envelope. There are distinct advantages to the use of two tubes as a single amplifier. In the first place, the gain of the combination is essentially independent of the load and the output impedance of the amplifier is low. In the second place, there is the advantage of distortion reduction by complementary distortion The voltage amplifier and the cathode follower have transfer curves with opposite curvature and the total distortion produced in the combination is considerably less than that found in either the voltage amplifier or the cathode follower alone. It may at first seem somewhat of a surprise to find that distortion decreases as one proceeds down the line of amplifier stages in such a connection but apparently it is exactly the sort of phenomena which Macdonald describes which is taking place. If some care is taken in selecting the operating points of the two stages, it will he found that a very low value of total harmonic distortion may be achieved."

An excellent article on this circuit can be found in the 1955 issue of Wireless Engineer, pages 29-31, "Constant H.T. Current Amplifier."
   I did not know about this circuit topology's grace-fallen state, but I do know that topology is linear, in fact more so than its constituent elements! A good deal of distortion cancellation occur when a signal travels from one triode into the same triode with equal voltage and current swings, but in anti-phase. The topic of complementary distortion reduction was a hot back in late 1950's when J. Ross Macdonald's article, "Nonlinear Distortion Reduction by Complementary Distortion," IRE Transactions on Audio, Sept-Oct 1959, came out. In a letter from R. A. Greiner in a following issue this point is made nicely:

   But really, the best course of action is to break out the soldering iron, high voltage regulator, oscilloscope, distortion analyzer, spectrum analyzer, and VOM and test these circuits yourself. Use a potentiometer for a load, so that you can readily measure the amount of distortion versus load impedance. Then measure the peak current into the load impedance and compare it to the idle current. The varition where a plate resistor is used is helpful in allowing ready measurement of the currents through the top and bottom triodes. I think you will be in for some surprises.