Treble cut when reverb turned up-VOX AC50cp

Hi guys,
I'm wondering if anyone can tell me what I should be looking for here-a friend has a Vox AC50cp guitar amp, and when you turn the reverb all the way up, there is a noticeable cut in the treble.  This is a problem when he is switching from reverb on to off.  I'm not sure if this is a "problem" or if this is just part of the circuit.  Any suggestions on what to look for?  The reverb circuit is solid state.  I haven't found a schematic, but I did find this schematic for the ac100cp...
http://www.ampix.org/albums/userpics/10003/Vox_AC100CPH.pdf

Thanks for any help!

when you turn up the reverb, you are mixing in the reverb side chain signal with the dry signal, so if the two channels are not balanced for tone, then as you increase the reverb, the sound of the reverb channel will dominate,

so it sounds like this is a normal thing,

this fender reverb unit that i just built has a tone control,

so you can match tone between the dry and reverb signals,

but with most reverb amps, all you get is one knob, so they try to get the balance right at the factory, but if something drifts, you have no way to compensate,

one thing to check would be the reverb pan itself, sometimes they have foam in there that can come loose,

and check to see how the reverb pan is mounted, i there are broken springs that suspend the pan, this can change tone, or if it is mounted with rubber grommets, check the rubber,

also see if the spring plate is suspended right, if it bottoms out against the pan, you can change the tone,

What is the Belton/Magic difference after IC209? How is this unit set up, you could try the other config to hear a change.

Good eye, Walter.  The "Magic" components were in.  Pulled them out, and the amp is a lot better now.  Thanks!

I did a search for Belton and Magic Reverb pans, I guess Vox used both and needed to have a way to adjust the circuit. I assume Magic pans are brighter or more sensitive. The recovery stage for the Magic Reverb has a 220pf and 22k feeding back to the inverting input and a 1Uf and 22k to ground.

here is a tiny image.

http://i93.photobucket.com/albums/l44/vogelelectronics/Revsnip.jpg