I have a 2 tube line stage with some stock Chinese tubes. The sound is a bit harsh and bright. I found some RCA's at the tubestore but the guy I talked to said he didnt know their sonic qualities as he seldom sells 5670's and has no customer feedback. These are the only NOS 5670's I have been able to find. Anyone ever used them?
Follow up: I scored some NOS RCA matched pair of 5670's from the tube store. Cheap too! $8 each and $10 to match them! They sound real nice even with low hours.Smooth with no harshness or brightness like the Chinese tubes they replaced.