Many folks who buy our tubes know that we use a special process to categorically rate our tubes so that players can select the tubes that best fit their preferred tones and styles. However, we get a lot of questions about our rating system, and what the numbers actually mean.

IMPORTANT BIAS NOTE: If you're replacing a tube with the SAME TYPE of Groove Tube (tube model and rating), you do not have to rebias your amp. In any other case, you should always have a qualified amp tech reset your amp’s bias whenever changing your tube type or rating number.



Early distortion, wide range, softer attack good for Rock and Blues solos.



Normal performance, great dynamic range/attack and best all around rating type for all styles of playing



Most dynamic range, most clean power/less break-up for power players, Jazz and bass amps.

Green Day

Nobody rocks the charts and the world's concert stages with more powerful punk-pop majesty than Green Day. They seemed to single-handedly restore the punk sound and ethos to the charts when they burst on the scene with 1994 major-label debut Dookie, which sold more than ten million copies and opened the floodgates for a U.S. neo-punk revival. Green Day, however, remains at the forefront - as popular today (if not more so) than they've ever been. Green Day was formed in the Northern California underground punk scene when two childhood friends, guitarist vocalist Billie Joe Armstrong and bassist Mike Dirnt (born Mike Pritchard), formed their first band, Sweet Children, in Rodeo, Calif., while both were only in their early teens. Drummer Al Sobrante joined in 1989, and Sweet Children became Green Day. Indie debut EP 1000 Hours was released in 1989, followed soon after by first album 1,039 Smoothed Out Slappy Hours. Shortly after its release, Tre Cool (born Frank Edwin Wright III) replaced...

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