Ruby Tubes 12AU7CZ is a high-grade, low noise, low gain tube with smooth mids and a mild top end. May be used for taming unruly amps.Wonderful in Hi-Fi and guitar amps. Very smooth and detailed with a great open sound. Solid construction and extreme attention to detail make this tube one of the best preamp tubes in production today.Ruby Tubes 12AU7CZ preamp tube is low noise, has sturdy construction, and great tone.