Groove Tubes GT-KT66-CQ Quartet Matched Power Tubes Low An exact copy of legendary Gold Lion valve from the Eric Clapton "Blues Breaker" Marshall combo Similar in design to the 6l6, KT66's are commonly used in boutique amplifiers such as the DR. Z Route 66 KT66's are known for their bold, firm, and fat tone characteristics Hand Tested &amp; Matched in Quartets (a set of 4 tubes) Limited Warranty Included