The schematic to the right displays the basic output stage configuration. The output tubes can be wired in triode mode or pentode or ultra-linear. The DC voltage present on the cathodes is due to the DCR of the transformer's primary against the idle current of the output tubes. In the schematic below, a suitable driver stage is shown. Since the output stage works as a push-pull cathode follower, the drive voltages needed are great. This means that both high gain and a large output voltage swing are required. The 6072s provide the gain and the 5687s provide the voltage swing and offer the required 50% power supply noise reduction….
I better stop now or I will have an entire article written. (A friend asked how I can write more than two or three articles per lifetime without running out of topics!) As for the tight lips, I am amazed by cloak of secrecy surrounding obvious circuits. I have seen a grown man reverently clutch a wrinkled sheet of paper with some super-top-secret circuit drawn in pencil by some exalted tube guru, whose name could only be whispered.
TCJ Circlotron Output Stage
And when I pried it free from his sweaty palms, I could not help but cry with laughter: a grounded-cathode amplifier that uses a 6FQ7! Wow! If you or anyone else try these circuits, let me know how they work out.