Groove Tubes GT-6L6-GE Medium Duet Amplifier Tube Faithful reproduction of original "clear top" '50s and '60s tubes Originally invented by RCA in 1936, the 6l6 Tube has been used extensively in Fender amplifiers since the 1940's The flagship of the Groove Tubes 6l6 Line Hand Tested & Matched in Duets (a pair of 2 tubes) Limited Warranty Included