Fender Groove Tube ecc83s Is a classic Euro type with medium to high gain and a linear frequency response. Very clear even tone with good bass character. This is the standard tube that was used in Marshall amplifiers and Vox amplifiers. For those that change first stage gain preamp tubes to change the taste and character of their amps (remember, this can be done in less than a minute without tools, adjustments, or a "tech"). This is one tube that should be in your basic toolbox. The basic tube sets generally are the 12AX7C, ECC83, and 7025 to cover a wide range of styles and tastes for most amplifiers.