Hi Sakahara,
I've owned the KR's and found the sound wonderful.They made my system sound fantastic. The problem was that they are not reliable. One of mine failed with less than 100 hours on it. The manufacturer did not stand behind them, and wouldn't replace it claiming I was responsible!?You can check out the archives on this tube as my experience was not unique.
I have tried a number of 300b's. I had Sophia, TJ carbons plates and a few I seem to have forgotton. The best I have heard is the Shunguag Black Bottle (Treasures)that I have settled on. They sound as good if not better than the KR's, and are reliable. I must have 1500+ hours on them.
I do wish to hear NOS WE's one day.
Regards,