If I understand correctly, The Taboo amp has the "Lucid" circuit because all amps running in Pentode form need a feedback circuit, and the "Lucid" circuit was an outgrowth of this.  But is it only Pentode amps that could receive a "Lucid" circuit?  So far as wiring goes, I see from the diagram that the "Lucid" circuit has nothing to do with the EL84 output tube. One end of the circuit attaches to the speaker end of the output transformer, the other end attaches to the cathode of the driver tube.  

But I know nothing about other considerations. Would a Triode or Ultra-Linear amp be stable with this circuit added? Would it have ringing? Would the sound retain it's clarity?