+1 for Shuguang 845B. My amp came with Linlai HiFi, their base intro level tube. OK but not distinctive. The Shuguang 845B much smoother, with nice balance, good strong bass, warmer but still neutral midrange and clean, clear treble. Pleasant linear sounding tube. Definitely an upgrade at a reasonable price. i paid $250 for the pair. NOS RCA, United and GE outrageous $$$, so won’t be rolling them in!
Have another amp that runs KR 300B XLS, spectacular tubes! But $1,000 pair. I would imagine the KR 845 would also be a spectacular tube. Thousands less than NOS RCAs. Maybe someday, but I’m happy enough with the Shuguang 845B to not order KRs anytime soon.