Output stage madness - inductances and other design considerations

[ostripper]

While reviewing various schema's and actually working on one of the circuits shown below (pix 1) , I wondered about the application of "strategic" inductances in the output stage. While working on the Harmon - Kardon 1500 , I was impressed with the fact that it overheated (thermal runaway) and only the fuses blew. with some new fuses ,caps, thermal paste , it had a wonderful sound and seemed to be "rock solid stable" (for a triple). I noticed the inductors in parallel with the basestoppers (pix 1 -L3/4 and R43/45) and researched their purpose. Pix 2 is another HK amp that got awesome reviews for sound/useability as well .. same L/R , but with a 22ga/2 turn ferrite bead inductor (.2 -.5uH ?)

Many searches later , after sifting through all the L/R references AT the OP (zoble , etc.) stage , I found this bit ...

1. - " The resistor (ignoring the "imperfections" of parasitic capacitance, lead inductance, etc., which is usually valid at audio frequencies) will have the same impedance at every frequency." , and 2. - " the inductor will have an impedance that goes up with frequency" .

This explains (sorta ) what will happen when this flavor of OP stage (both pix 1 and 2) is added to the main feedback loop of the amp. My "take" is that the phase margin will be increased and the gain will be attenuated with increasing frequency. In the case of the harmon Kardon designs , this allowed for 15+ years of hard use /abuse (VERY stable) . Mr . Cordell had me add inductances to the driver collectors .. Post 108 Self type 3 EF (hybrid triple)... any pointers ??
to INDUCE instability , here we see the opposite..

Onkyo, (pix 3) wrapped the whole OP in the miller loop (2 - pole) using a small toriodial inductor to isolate the miller loop from the main NFB ... strange .

I have not had any "trouble with triples" (doug self topic) , but would like to push the "margin" as far as possible in making this OP as DIY ' able as the common EF. Most of the Triple OP designs use older BJT's with low Ft (MJ15003/4 - leach). Subjectively , some .. "uncle charlie" - DX , say the (triples - leach amps) burn up or have weak Bass. I have noticed the opposite , VERY powerful bass ,extreme reliability , and the almost zero loading on the voltage stage - very desirable attributes. Can't think of any other way to run 5-6 pair OP's off of SMD 2ma voltage stages.. .

OS