Anyone who has used the mu follower topology and likes it, must also understand one of the frustrations with the circuit is the heater supply for the top tube.

Why is this a problem in the first place? Well, I can think of two reasons... hum suppression of the heater supply and heater to cathode breakdown potential.

One of the tricks to suppressing hum on the heater I like to use is to lift the heater to some positive potential above the cathode potential (Figure 1). That is no real problem where the cathode is near ground, but when one cathode of a dual section tube is floating higher up in the sky, raising the heater voltage to where the top heater is above the cathode may inavertently cause heater cathode breakdown of the bottom tube.

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With a lower high voltage power supply,...