Groove Tubes GT-12AU7 Select Preamp Tube G Country of origin: China 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