dave robinson wrote:Thanks for that Roger, is there anything about those that is special or makes them likely to be hard to replace ?
As you probably know, a 1 megOhm log pot (volume) is standard stuff. I replaced the pot in my original 1967 pedal back in the 1980s. The original had a steel shaft (I still have the defective pot somewhere). The replacement (from Maplin or somewhere) had a nylon shaft (which worked better because you could get the pinion wheel to grip better).
It's the double-ganged pot for the tone control(s) which is non-standard. One pot is logarithmic and other anti-logarithmic (wish I could remember which is which). That set up allows the bass to be cut whilst the treble is being let loose (at one end of the travel). And of course, vice-versa at the other end. It's for this reason that the pedal cuts signal at any setting - there's always something being cut at every pedal position.
Roberto was at one time negotiating with Allen-Bradley to recreate the DeArmond's double-ganged pot, but it was one of the things that fell by the wayside.