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.

John Spiker / Tenacious D

Columbus, Ohio native and longtime member of Tenacious D, John Spiker moved to LA and got his start in the studio engineering for John King of the Dust Brothers. Soon John was playing bass and guitar with everyone from Steve Earle (Grammy winning Washington Square Serenade, Townes), Beck (Guerlito), Joan Jett (Runaways) and Filter to name a few. John also has toured and appeared on various late night shows worldwide with such artists as Tenacious D, Filter, Trainwreck, Shane Harper and Ronnie Vannucci's Big Talk. When not on the road, John can be found in Los Angeles engineering and producing for various artists, as well as keeping busy as a session bassist.

View Artists Profile