Wolf,
Before doing the SE upgrade to my Ref 150, I bought 2 matched quads of KT-150s from a respected tube vendor.
Some pairs biased pretty closely; others were off by as much 6 or 7 mVs, which as I mentioned somewhere, is pretty close to the boundary of ARC's recommended range (between 57 to 73 mVs).
IOW, if a set tube is biased at 65 mVs, the slave measured at 71 or 72 mVs. The max spec is 73 mVs.
Anyway, I only put about 200 hours on the KT-150s. Am I offering them for sale? Not sure. ARC charges $200 per KT-150.

