Adding both circuits together allows us to create a fully DC coupled hybrid amplifier. The amplifier shown below illustrates what is possible. The current variations through the input tube drives both output MOSFETs. So as not to confuse too many readers, no feedback loop is shown, but one could easily be added by bridging the bottom triode's grid to the amplifier's output. And a DC servo-loop can be added to the bottom MOSFET's gate, which would eliminate any DC offsets and the need for the potentiometer at the bottom triode's cathode.
    The 5 volt zeners protect the MOSFETs from too great a current draw in the case of a shorted output. The 7370 is a 40 volt heater version of the 5687, which allows attaching the heater across one leg of the power supply. The BUZ900 might not be the best choice, as a greater gain could be realized by replacing the 100 ohm resistors with 400 ohm resistors. But the relatively low gate threshold voltage (usually an advantage) of this device prohibits using the higher value resistors.

    The circuit shown above is also a cascode design. The bottom triode's cathode-to-plate voltage is locked by the MOSFET's source. (The plate resistor could be replaced with a top triode configured as a current source to decreased power supply noise making it way to the output.)

   Any signal presented to the bottom triode's grid will provoke a current variation through the triode, which cannot find a exit path through the plate resistor, as the MOSFET holds a fixed voltage across the plate resistor, which in turn, fixes the current through the resistor. So where do the current variations go? Through the MOSFET and then into the 100 ohm resistor is the only path. What happens is that the MOSFET's source moves ever so slightly in response to these variations (the MOSFET has huge amount of transconductance compared to the triode) and this movement results in a varying current through the MOSFET. If the triode were pulled from its socket, the MOSFET's idle current would double, but the voltage across the 5k resistor would barely change. Locking the plate voltage is the main point of a cascode circuit. In fact, his circuit functions much like the previous one save for the phase inversion at the top of the 100 ohm resistor.   

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