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But here they are the same value
Yeah, that don't smoke neither.
The input grid only has to be driven "sorta good". The off-side grid must be NAILed to reference; even a slight signal here upsets your balance at lower frequencies.
Which is NOT bad for guitar. That isn't about "perfect balance". You could try 0.1u, but the 0.01u may be giving a phatt tone on the lowest guitar notes which may be good.
I have no idea what Analag's point is.
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guitar amp designers advocate NOT to use NFB
There's many sides to this. A BIG point is what kind of speaker you use. Naked pentodes driving open-back cabinets with stiff cones are liable to bass-slap. I think the original point was to add just enough damping to get the bass-peak down so it did not make rude noises on your lowest note. Later fashion in Hi-Fi design and also cabinets tends to favor more NFB, right up to early Sunn with Hi-Fi damping. Of course transistors damp great and clean, and there is some rediscovery of loose no-NFB amps.
Make the NFB variable. Understand that the "best" degree of NFB depends on your speaker-rig, as well as your style and religion. I tend to worship high-NFB, but I must admit the zero-NFB Ampeg VT-40 is a heck of a guitar voice.
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P.I.plate resistors in the fender blackface had one 100k and one 82k, this was to set it off ballance slightly for a meaner tone.
They "improve" balance. The nearside plate makes more signal than the offside plate. The 82K reduces the output of the nearside. The overall NFB into the tail also
seems to improve balance, though it was probably a mistake which worked good.
http://300guitars.com/index.php/articles/article-demystifying-the-phase-inverter/
Yes, a good re-drawing, simplified. The drawing lacks stuff to get a good operating point. The text mis-states the reason balance is flawed... at least using Fender-like values, the imbalance is because the tail resistor diverts signal current. But it is NOT useful to think too hard about gitar amp balance.
PUSH-pull works fine, and may be sweeter than exact-balance push-pull.