Hi Pete,
I have the white knob model. Other than color are there any major differences electrically?
Steve
Different production runs. Minor changes to component values in various parts of the circuitry. Polytronics, like a lot of other manufacturers during that era, made changes on the fly. Some were documented, most were not, since most of the time large amounts of manuals were already printed before changes were made and they generally didn't update the schematics for consumer use. I have both a white knob and black knob PC-6. Also have the PC-2, PC-62, and a prototype Polytronics linear for the PC-6. They also made a great line of CB sets, and business CB sets. Lafayette Radio HB-333 CB set was also made by them.