Peavey Artist VT resonance & presence mods

[ozymandias]

Can anyone here help me understand what's happening with my attempt at adding resonance and presence controls to my Peavey Artist VT, please?
I'm trying to filter out frequencies in the Negative Feedback Loop between the Output Transformer and the Phase Inverter.

Image 1 shows this part of the circuit, and image 2 is zoomed in on the area that I'm modifying. (Note though, that I have found this to be wrong; examination of the board shows that the circuit is actually as shown in image 3).

Image 4 shows the mods I am trying out, but I am getting unexpected results. If I put the mods between the OT and IR23/IC25, the resonance works but the presence doesn't. If I put the mods between IR23/24 and IC24 the presence works but the resonance doesn't. I'm going to try separating the presence and resonance mods and putting them where they seem to want to be, but I was expecting them to both work at the point between the OT and IR23/IC25. Can anyone shed any light on why this isn't happening, please?

[loudthud]

What you want is something like this:

[Enzo]

I can't wrap my head around this at the moment, but if you replace IR24 with the presence pot and cap, you have broken the voltage divider previously formed by IR23, IR24. A 220nf cap limits the freq range for its reactance.

It looks like you may have lifted the feedback circuit from a later PV amp like the150 series et al. Note that in teh Artist, the feedback feeds into the side of the phase inverte, while the feedback in the 5150 amps feeds into a cathode further back.

[ozymandias]

I can't wrap my head around this at the moment, but if you replace IR24 with the presence pot and cap, you have broken the voltage divider previously formed by IR23, IR24. A 220nf cap limits the freq range for its reactance.

It looks like you may have lifted the feedback circuit from a later PV amp like the150 series et al. Note that in teh Artist, the feedback feeds into the side of the phase inverte, while the feedback in the 5150 amps feeds into a cathode further back.

Sorry, but I've very limited experience so the significance of the side/cathode feed into the phase inverter is not something I'm aware of (nor can I find anything about it with google). Is the fact that this is a side-feed going to stop me from doing this mod properly?
The mods I'm trying are based mostly on the Valve King 212.
Just wondering what that 39pF capacitor is doing. I'm guessing it's damping down any high frequency oscillations, but could it also be affecting the attempted presence mod by passing frequencies to the PI rather than to ground (seems unlikely to me, but just a thought).?

Thanks.