So it seems to me that you can ONLY get 500k concentric/stacked pots (meaning, both of the pots that make up the stacked pot have a 500k value). Does anyone sell decent quality concentric pots of other values? Pardon any ignorance here, but would the difference in tone between 250 and 500k pots be really significant? Please feel free to school me on the whole concentric pot thing. It's something I'm really curious about.