Groove Tubes GT-E34L-SD R7 Duet Matched Amplifier Power Tubes The heat wings attached to the plate give our version of the original EL34 15-20 percent more power Interchanges in any EL34 application and stays tight and robust all the way up to full power Highly dynamic, big low end and runs cooler for longer life; Amazing headroom, killer tone and all of the great features and characteristics of the EL34 design Hand Tested & Matched in Duets (a pair of 2 tubes) Limited Warranty Included