I recently picked up a beater 500-C to tke me through those lonely winter nights. A visual examination brought me to the volume pot which didn't seem right because it wouldn't mount securely even after trying to tighten the securing nut. Upon closer examination I saw that the pot plate closest to the face plate was not flat as is all of the pots I've come across. Deciding it was a repair replacement I removed it in favor of a replacement pot & switch I had on hand. The replaced pot had the correct Fisher part number BUT with a CX as a suffix. I guess it came from a CX pre? Anyone can confirm??