Treble shunts ?

[12AX7]

I could use some schooling one this subject, specifically what is the difference between shunting highs to ground vs caps on the plate resistor to the power rail. I have them on my peavey classic 30, the newer version. But the older version doesn't have them. I have been told they might be to stop oscillation but the 2 versions are very close so them why on one and not the other. So i removed them because i felt my amp's top end was mostly in the lower treble ranges and could use some sparkle in the higher registers. Removing them did help, but very little. What are your thoughts on this in the schematic i'm posting? I'm probably going to do more like swapping the 470pf ground shunt after the pre pot for a 100pf. I have done that before but had added a bright cap to the pre pot so it was overkill. I removed that since and thats why i may go back to the 100pf in place of the 470 after the pre pot ground. That had more effect than removing both plate caps. What are your thoughts on this?
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