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 JJ KT88 Matched Quad The JJ Electronics KT88 has beautiful imaging and nice full bass response. Great for the Dynaco MkIII. KT88JJMQ SOVTEK 6550 MATCHED PAIR SOVTEK 6550 MATCHED PAIR SOV6550MPAIR SOVTEK 6550 MATCHED QUAD SOVTEK 6550 MATCHED QUAD SOV6550MQUAD 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. 6550-TS-MP 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. 6550-TS-MQ TUNGSOL 6550 REISSUE reissue of the venerable TungSol 6550 tube. Well regarded by those who've tried them so far. Price is for a single tube. tungsol6550single SOVTEK KT88 SINGLE TUBE SOVTEK KT88 SINGLE TUBE SOVKT88$54.95 KT90EH ELECTRO-HARMONIX MATCHED PAIR - SPECIAL ORDER KT90EH ELECTRO-HARMONIX MATCHED PAIR - SPECIAL ORDER - PLEASE ALLOW APPROX. 1 WEEK kt90ehmp Triode, USA Customer Service M-F 9AM-4PM CT 1-800-774-3201 Email us Anytime: questions@triodestore.com