I am selling one matched pair of New Telefunken 12AU7 ECC82 smooth plate tubes with diamond bottom. These tubes are specially selected by Tektronix to use on their test equipment. Same serial number on both tubes. Tubes tested on my Western Electric KS-5727-L1 with no shorts. Tube measure 2400/2550 and 2425/2550 where minimum is 1385. Please email for any questions.