Variable Mu Retube Kit Version APlease read the full description: This kit is only for Manley Variable Mu's (and mastering versions) with the serial number between MSLC000 MSLC123 and MSLC7124 MSLC7264. We no longer provide the original 6386 tube used in these units, they have been substituted with 5670 tubes but your unit MUST be upgraded to take this substituted tube, or you can find the original 6386 elsewhere. This kit includes (2x) 5670 tubes for input, (2x) 5751 tubes for