Tightly matched pair of IEC/Mullard 12DW7/7247 twin dissimilar triode vacuum tubes made in Great Britain. Same section of each tube tests 1950 and 2037 uMhos with a baseline of 1050 uMhos. The other section of each tube tests 2845 and 2926 uMhos with a baseline of 1900 uMhos. Tested on Hickok AN/USM-118B.