Groove Tubes GT-6550-CQ-R2 Quartet Power Tubes Popular alternative to KT88 and KT90 tubes (when compatible) Clean and clear sounding tube with amazing headroom Originally designed for Hi-Fi amplifiers by Tung-Sol, 6550 tubes are commonly found in vintage Fender, Sunn, and Ampeg bass amps Hand Tested & Matched in Quartets (a set of 4 tubes) Limited Warranty Included