The Sylvania 6SN7-GTB tube is a nice moderately priced alternative to other rare Sylvania 6SN7 tubes. This Sylvania 6SN7GTB tube was produced and packaged in the late '70's. It has a "coin" base and black triangle-plates. It has good detail, highs, and tight bass. They are a natural sounding tube with nice warmth, but not overly warm.
The Sylvania 6SN7 Tube Types are fantastic upgrades for Rogue 99 Magnum preamps, Cary SLP 98P / SLP 98L and SLP 05 preamps, and Atma-Sphere preamps.