Brand new vacuum tubes made OEM for Mesa Boogie by Shuguang to Mesa's exacting specs and tolerances. They were to be used in new amp production and are not labeled or packaged to be on a sales shelf. Beam power tube/valve numbers 6L6GC, 6L6GCR, 6L6G, 6L6GA, 6L6GB. These tubes are compatible with 5881 and any 6L6 . I have tested and matched these on a RoeTest professional computer testing system, the best tester available today.