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?
https://el34world.com/Forum/index.php?action=dlattach;topic=33458.0;attach=124838

[HotBluePlates]

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. ...

The "Power Rail" is also "AC Ground" if the filter caps are still working well.  So technically there should be "no difference" other than it may be physically-easier to install a capacitor-to-"Ground" in one or the other places.

... shunting highs to ground ... caps on the plate resistor ... I have them on my peavey classic 30 ... I have been told they might be to stop oscillation ... 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. ...

The Classic 30 has a Clean channel that is 2 gain stages followed by a Tone Stack, and a Dirty channel that is 4 gain stages (followed by the same Tone Stack).

   - The capacitors to "remove highs" (whether going straight to ground or placed across plate load resistors) were likely added to reduce noise & harsh treble with the 4-gain-stage Dirty channel in mind.

   - You might tinker C24 (1.5nF to ground) to see how much it impacts treble-reduction, along with C70 (100pF to ground).  This is a tricky spot, because R48 (2.2MΩ) is negative feedback that helps set-level for the Reverb side-chain, and the relative-level of the Dry path coming via R29 (150kΩ) and R18 (220kΩ).

   - Be aware that "sparkle" may also be hampered/enhanced by the speaker used; many Celestion-type speakers are darker than you might suspect if you do a direct-swap for a Jensen-style speaker.  It's pretty hard to overcome speaker-voicing (whether to skew for "better Cleans" or to skew for "smoother Distortion").

[12AX7]

Thanks. yeah, i have wondered about c24 and wanted to try removing it altogether or trying different values, but it;s realy had to get to. I'm liking it right now but i hear ya about speakers. I already tried one that had i liked it and kept it i likely would have put those caps back to stock.

[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. ...

The "Power Rail" is also "AC Ground" if the filter caps are still working well.  So technically there should be "no difference" other than it may be physically-easier to install a capacitor-to-"Ground" in one or the other places.

... shunting highs to ground ... caps on the plate resistor ... I have them on my peavey classic 30 ... I have been told they might be to stop oscillation ... 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. ...

The Classic 30 has a Clean channel that is 2 gain stages followed by a Tone Stack, and a Dirty channel that is 4 gain stages (followed by the same Tone Stack).

   - The capacitors to "remove highs" (whether going straight to ground or placed across plate load resistors) were likely added to reduce noise & harsh treble with the 4-gain-stage Dirty channel in mind.

   - You might tinker C24 (1.5nF to ground) to see how much it impacts treble-reduction, along with C70 (100pF to ground).  This is a tricky spot, because R48 (2.2MΩ) is negative feedback that helps set-level for the Reverb side-chain, and the relative-level of the Dry path coming via R29 (150kΩ) and R18 (220kΩ).

   - Be aware that "sparkle" may also be hampered/enhanced by the speaker used; many Celestion-type speakers are darker than you might suspect if you do a direct-swap for a Jensen-style speaker.  It's pretty hard to overcome speaker-voicing (whether to skew for "better Cleans" or to skew for "smoother Distortion").

By the way, am i correct in assuming the reason you mentioned C24 is because it may be a better way to add top end because it's AFTER the gain stages vs IN the gain stages where highs can become harsh when it's multiplied?