The Groove Tubes GT-12AU7 preamp tube is based on a design from the Ei factory in the former Yugoslavia. The GT-12AU7 is an excellent quality large-plate European-made driver tube, styled after the famous Telefunken line of dual triodes. The usual application for a 12AU7 tube is as the phase inverter that drives the power tubes. These are very well matched, and so are highly recommended for Ampeg SVT"s and other amps using this tube as a phase inverter. Also commonly used as phase inverters in McIntosh Hi-Fi amps, some Ampeg amps, and will yield the most clean headroom in many amps. In the latest Fender Pro Series amps such as the Pro Reverb, Concert, and Twin, this tube in V2 (or a 12AY7), will drop the gain of the gain channel where some feel the tone is of a less intense or "buzzy" character. This will then allow a much wider range in the sweep of the volume and gain controls of this channel. Country of origin: ChinaCountry of origin: China