Picked up this Brownsville Wah via eBay.
This unit powered externally via a 3.5mm mini jack (pos tip).
The first mod as replacing it with the 2.1mm (neg tip) standard and removing the battery clip).
The circuit was identical to most inductor based wahs I've seen.
Cleaned the pot and did the following mods:
Q Vocal Mod - Changed R1 to 100K (originally 33k)
Increase Gain and Bass Mod - change R12 to 330R (from 390R)
Volume Mod - Change R3 to 47k (from 68k)
Midrange Mod - change R4 to 2.7k (from 1.5k)