I'm building something very much like that right now. On the bread board the sound is good if I keep the volume way down. I'm using some smaller OPTs. Then I connect ot this huge 11 pound OPT I have and it is very good. So far no NFB. I built the triode version and it's OK but VERY limited power. the Pentode version worked better. I used 100R screen grid resistors. (they make great fuses)
I've also tried very small about of local NFB around the first triode and is knocks distortion down. The 12AT7 is best if you must use one tube from both stages but in stereo yu can use one duel triode for both left and right splitter and one to input. In this case lots of things work. 12AX7 input with mild local NFB and 12AU7 splitter. or 12at7 all around. Or even 12au7 all around and no local feedback.
But the schematic as drawd is pretty good based on above breadboard experiments.
In the end the quality of the sound will depend mostly on the quality of the transformers. All this other stuff, like even which input tube is just "details" compared to transformer selection.
I don't know why we call them "tube amps". They should be named after their biggest, most important and expensive part. We should call them "iron amps". A small EL84 amp like this can have $250 worth of transformers ann about $80 in tubes. A 4x difference.
Joking aside, I think the attraction of tubes is that they still have a sound. SS amps don't they are all designed to a THD of approximately zero. But if you want to work in a genre where there is room for infinite creativity and still things to do build a guitar amp. Musical instruments produce sound, HiFis only reproduce sound. I like to do both. But I buy SS amps, little point in building one. In fact HiFi would be useless if not for musical instruments
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