@Kim Christensen : What would be the feedback back that " the 3 opposing output transistors would turn on hard"?
Any info available on the web that would explain the working of the attached schematics especially the negative feedback path?
In this Amplifier, the negative feedback path is via R028 (From the speaker output back to the differential input) The AC voltage gain is set by the ratio of R028 to R018.
Suppose the DC voltage at the output was too high. This would increase the current fed to Q002's base via R028 turning it on more. Because Q002 and Q001 are configured as a differential pair, this will make Q001 to turn off which turns Q007 off, which lowers the voltage at the base and thus emitter of Q012, this also lowers the voltage on the bases, and thus the emitters of Q026, Q013, & Q014...
The opposite (On vs OFF) happens with the mirrored circuitry below (Q004, Q003, Q011, Q015, Q025, Q016, Q017)
Note: When I say on and off, I mean On = passes more current.. Off = passes less current... Fully On/Off would be clipping in an audio amp, but it's easier to explain that way.
To understand these types of circuits better, look up:
"differential amplifier" (Q001 & Q002 for example)
"constant current sink" (Q010, R026 & D003)
"push pull audio amplifier"