Margaret Diekemper

A Wrong Turn

A wrong turn A cathode-follower output stage can excel, but only if it is given a pure input signal—a very-large pure input signal. Yes, indeed, the problem of giving the output stage the required drive signal is a big one: for what shall it profit a man, if he shall gain the lowest distortion output stage, but loses the driver stage’s integrity? Verily. Remember the output tube(s) grid must see a signal larger than the cathode will swing: the inverse of the cathode follower’s gain, in fact. Thus, a cathode follower gain of 0.9 would require a grid signal that is 1.11 times larger that the desired cathode swing; for example, 111V peak volts in for 100V peak volts out, 222V peak-to-peak for 200V peak-to-peak.