5881 and 6L6WGB designations are interchangable and the tubes may have either or both designations. Lightly used, test as new. NOS (unused) examples are very expensive, so this is a great way to get in on the TONE! The bases are various shades of brown and may not match. These have a mixture of different brand names including, Tung Sol, RCA, GE, Philips, Sylvania, CBS, etc. All are identical and made by Tung Sol. Matched pairs may comprise 2 different brands but the tubes are identical and made by Tung Sol. First priority is electrical matching.