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.

low

1-3

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

Medium

4-7

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

High

8-10

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

J Mascis

Indeed, Mascis is one of today's foremost exponents of the Jazzmaster. A surf staple in the'60s and a punk fave in the'70s, the guitar had become something of a fringe model by the 1980s. But the Jazzmaster was given new life in the'80s,'90s and beyond by Mascis, who took the instrument to a new place with his feedback-drenched, distortion-laden band, right-coast grunge pioneers Dinosaur Jr. Mascis (born Joseph Donald Mascis Jr. in 1965), bassist Lou Barlow and drummer Emmett "Murph" Murphy came blasting out of Amherst, Mass., in the mid-1980s with their debut album Dinosaur blazing an acclaimed indie rock trail with albums You're Living All Over Me (1987), Bug (1988), Green Mind (1991),Where You Been (1993), Without a Sound (1994) and Hand It Over (1997). Mascis assembled a new band, J Mascis and the Fog, in 2000, but when Dinosaur Jr. came back from extinction for a 2005 tour and released a new album, Beyond, in 2007, Fender knew it was high time to recognize one of its rare Jazzmast...

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