While trying to order replacement potentiometers for this project, I had some difficulty sorting out the pot values.
All the schematics I found online show the pot values to be 1MΩ and 10KΩ, but the pots in my script logo 1977 Distortion+ measure 500KΩ and 56KΩ..
Google search turned up this post from DIYStompboxes.com that cleared up everything.
DIYStompboxes wrote:
After seeing discrepancies among various schematics, I spent way too many hours one night looking into the pot values for the D+. Seems the earlier "script" models used 500K for gain and 50K for volume, but I could never 100% verify that because the pots they used had part numbers without resistance values stamped on them. Maybe starting around 1980 or so, the pots were changed to 1M and 10K. The value of the gain pot doesn't really matter, the 1M is just able to get a little cleaner than 500K, but like you said the volume pot value does make a difference.
FWIW, the 50K volume pot actually measures right around 10K in circuit, this may have added to the confusion over the years, from people who own originals but don't want to unsolder anything.
(Edit: It's probably not just a coincidence that the "script" MXR Dyna Comp also used C500K and A50K pots.)
(Edit 2: Looking at some pics online, seems for at least a period in the mid- to late-70s, the part numbers stamped on the pots were MXR9471 for A50K and MXR9479 for C500K. You can see these part numbers in gut shots of both Dyna Comp and Dist+ pedals.)