I'm not 100% sure,but someone told me years back that they were made by RCA,even if they have different brands stamped on them.
Tube rolling for Musical Fidelity Nuvista M3?
Has anyone tried tube rolling the 6CW4's tubes in the pre section of their Nuvista M3? The tubes are very inexpensive so I'm hoping somebody can share their tube rolling experiences with this unit.