All 6550 & KT88 include 24 hour burn in & matching,and of course include our 6 month replacement warranty. 6550kt88kt90 JJ KT88 Matched Pair The JJ Electronics KT88 has beautiful imaging and nice full bass response. Great for the Dynaco MkIII. KT88JJ$73.99 JJ KT88 Matched Quad The JJ Electronics KT88 has beautiful imaging and nice full bass response. Great for the Dynaco MkIII. KT88JJMQ$147.99 SED =C= 6550 Matched Quad Nice Detail and seperation. Very Balanced sound. This is a very consistent and reliable tube, one of the best current production 6550's. Used in Audio Research amplifiers, also works well in Dynaco MkIII, Some Marshall amplifiers and Leslies. wingc6550MQ$123.99 SED =C= 6550 Matched Pair Nice Detail and seperation. Very Balanced sound. This is a very consistent and reliable tube, one of the best current production 6550's. Used in Audio Research amplifiers, also works well in Dynaco MkIII, Some Marshall amplifiers and Leslies. wingc6550MP$61.99 6550 Tungsol Reissue Matched Pair New Russian made reissue of the venerable TungSol 6550 tube. Well regarded by those who've tried them so far. Price is for a matched pair (2 tubes) and includes factory matching & burn-in. 6550-TS-MP$68.95 6550 TungSol Reissue Matched Quad New Russian made reissue of the venerable TungSol 6550 tube. Well regarded by those who've tried them so far. Price is for a matched quad (4 tubes) and includes factory matching & burn-in. 6550-TS-MQ$135.90 Triode Electronics Inc. 5633 W. Irving Park Road Chicago IL 60634 USA Ph 773-427-8823 (773-HAS-TUBE) Fax 773-327-5652 Open 10:30 AM to 5 PM CT Monday-Tuesday-Thursday-Friday