The Groove Tubes Gold Series GT-ECC83-S tubes are specifically designed and tested for musical instrument amplification and standard equipment on many Fender amplifiers. These are ideal preamp tubes for attaining outstanding and consistent performance when mixing and matching. in order to get a signature tone from your amp. These tubes have a huge amount of gain with terrific output, making them a great choice for driving modern, complex high-gain circuits. With a tight, strong and relatively bright tone, the ECC83s can really liven up a weak or tired old vintage amp or a new amp with stock tubes.