The circuit above uses the coupling capacitor and two resistor voltage divider to DC bias correctly the cathode follower. The gain is close to unity and output impedance is low enough not interact too greatly with the filter components. The diode serves to protect the 6N1P at turn on. The coupling capacitor can become part of the crossover. For example, bi-ampped satellite loudspeaker might require a 100 Hz crossover point between it and the subwoofer. In this case the .22µF capacitor must be replaced with a 3183pF capacitor. (The two 1M resistors are in parallel, thus the terminating resistance for this capacitor is 500k.)
     A third possibility is to make a hybrid crossover, tubes on top and FETs on the bottom. The circuit below uses a DC power supply to power both the heater string and to load the cathode followers.  The constant current source can be the two lead FET current sources such as the 1N5314 or CRO-470. (Many tube fanciers will tolerate a solid-state device, but only if it has two leads, strange but true.)

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