change the 6.8k resistor that's soldered between the left lug of the
bass pot(s), (as you look at the back of the pot), to 10k and it will be
as if the Mid control is there and dimed...
 
Les
You can even go further than that and use 12K, 13K 15K, etc. The
best solution is to temporarily connect a 25K pot wired as a variable
resistor, find the sweet spot (to your ears), disconnect the pot
(without moving it), and measure the resistance. Then solder in a
resistor or combination of resistors which give a net resistance that
comes very close to what you had measured.
 
Actually, that stock 6K8 fixed resistor is equivalent to a stock Fender
midrange control set to to more like 8 or 9, rather than approx.
halfway up. This is because the 10K midrange pots used in Fender
amps are audio taper, not linear taper. When set around halfway,
these pots give a resistance of only about 2 or 3K, not 5K.
 
While you're in there, you might want to try experimenting with
removing the 47p bright cap soldered onto the lugs of the vibrato
channel volume pot. The cap adds a nice shimmer at lower volumes
but sometimes can make the seem amp too bright. Some people like
it there, others much prefer it taken off.
sonic

I have tried a 100k audio pot for some crazy adjustabl gain boost, and
you cound hook it up to the tremolo jack on the back as a foot
sw.able boost! I have a old Mesa foot sw. with a 100k pot in the foot
sw. when I plug the sw. into the amp, it kicks in this 100k circuit,
withit unplugged, it is stock. You can do it either way, as a pot in the
amp like you have or both, you could wire it up so the 100k bypasses
the 10k pot too. Just some crazy ideas to think of...  The 100k will
get you close to the Santana tone!
ed