About Groove Tubes®

For over 30 years, Groove Tubes have been trusted and demanded by touring professionals and their techs around the world. Groove Tubes started in southern California, and through innovative design, rigorous selection and testing, GT-powered amps have rocked the world in some of the most famous rigs ever played from studio to stage. Combining our passion for music with the science of sound, the Groove Tubes team still employs the same testing, grading and matching disciplines that continue to deliver flawless performance every time.

How We Get That Groove Tubes Sound

Guitarists both yesterday and today can be linked by one piece of equipment: The tube amp. With all the strides in transistor amp technology, guitarists still prefer tube amps. Why do tube amp designs sound and feel differently from solid-state? Simply, tubes work differently.

What is a Tube? A tube is an electronic device consisting of a minimum of four active elements: a heater (filament), a cathode, a grid and a plate. All sealed in a vacuum glass enclosure to prevent parts from burning. Once heated, the cathode begins to emit electrons, which flow from the cathode (which is negatively charged) toward the plate (which is positively charged). The grid’s purpose is to control this flow, in effect, acting as a valve.

How do Tubes Work? When the guitar’s pickup produces a small voltage (the result of the string vibrating in the pickup’s magnetic field), this signal is applied to the grid, which causes a large current flow from the cathode to the plate.

Because of this, a correspondingly large voltage now appears at the plate. A portion of the amp’s electronic circuitry, the grid bias control, adjusts the proper voltage setting of the grid. When the grid bias is properly set, the tube is balanced to the circuit, and therefore produces a clean, powerful signal. The plate is connected to an output transformer, which matches the impedance to that of the speaker.

How do Tubes Distort? As the signal emitting from the plate approaches its maximum potential, the tube gradually begins to react less and less to the original input signal. This results in a type of compression of the signal, and the signal becomes cut off or “clipped.” Tube distortion (“clipping”) occurs gradually, producing low order distortion which compliments the original signal, creating a warm sound. This is also why it’s easy to move between clean and distorted tones.

Download Groove Tubes Process PDF

GT Rating System

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.

Groove Tubes® Power Tubes – Dynamically Energized™ and Performance Matched™

These pass every Groove Tubes premium certification for micro-phonics, hum, noise floor, physical operation and performance characteristics. We also analyze and match the gain-to-distortion ratio on a dynamic basis, assuring a powerful, singing tone that is rich in harmonics and balanced for longer sustain, wider frequency response and a more musical amplification experience.

Groove Tubes are quite simply the best 8-pin pentode tubes you can buy that are specifically designed and tested for musical instrument amplification. Sold as single tubes, matched duets, quartets and sextets, Groove Tubes are standard equipment on professional Fender® tube amps.

Matching power tubes has been part of tube history since the beginning. Power tubes usually work in pairs, and we have developed proprietary selection and matching procedures. This includes special fixtures, processes and software, exclusive to GT.

Traditionally, power tubes are matched for output power only. In reality, the POWER output of tubes varies little, so testing strictly for power output is a rather meaningless exercise. What we do at GT is a much more involved test of the distortion and TONAL characteristics of the tube. Surprisingly, this is where tubes can vary quite a bit, even within the same model, factory and production run.

Groove Tubes has developed a procedure that combines valid, scientific comparison and exclusive methods that take into account the tonal characteristics of tubes for use in instrument amplification.