Below are two circuits designed in ignorance of the need for an appropriate balanced drive signal for each output device. Variations on these circuits are common, but all share the mistake of ignoring that the top output device effective drive voltage is altered by the influence the output voltage across load impedance makes. In other words, output signal effects the drive signals.       

    Now let's return to OTL push-pull output stages. The devices can be perfectly matched, but unless each receives the appropriate grid voltage swings, the output will be distorted. In turn, the appropriate grid voltage swing is dependent on the load being driven and few loads have a consistent impedance cross the audio band. I am stressing this point because many commercially successful amplifiers have been designed in complete ignorance or misunderstanding of it. And since tube audio design is not taught in schools anymore, most tube fanciers use schematics as textbooks. (You can imagine what happens when the textbook has a typo in it as many do). So, if you wish to understand both OTL and hybrid circuits, you must understand how the output devices must work equally, i.e. complementarily to deliver an undistorted output voltage into the loudspeaker.
     Since the OTL or hybrid output stage can use either tubes or solid-state devices, a block with "N" in it will be used in all the following circuits.

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