TJ and Sophia (and Full Music) are the same tube, yes, but Sophia tubes are specially culled, i.e., they are the best of that factory's production.
KR makes an 845 tube and I would expect it to be the best of currently available tubes. KR had a bad U.S. distributor for a few years, which resulted in KR's reputation in the U.S. taking a hit, but their new Ann Arbor-based distributor is fine. E.A.T. and Emission Labs, the other two Prague tube manufacturers, don't make 845's.
While I don't want to say that all Chinese tubes are crap - the Black Treasure stuff out of Shuguang and the TJ / Full Music / Sophia tubes can be quite good - I believe that KR and E.A.T.'s production tends to be a lot better. It can vary by production run, however, as tube manufacturing is largely artisanal and like everything else that's hand-made, a worker has good days and bad - there can be bad quality production runs from the more prestigious manufacturers, and good quality runs from the crap manufacturers - you have to have a reputable vendor to ensure that you don't get the "runts of the litter". Why are there two different prices and two different warranties offered by some vendors for what appears to be exactly the same tube? The more expensive ones with the longer warranties tested better.
KR makes an 845 tube and I would expect it to be the best of currently available tubes. KR had a bad U.S. distributor for a few years, which resulted in KR's reputation in the U.S. taking a hit, but their new Ann Arbor-based distributor is fine. E.A.T. and Emission Labs, the other two Prague tube manufacturers, don't make 845's.
While I don't want to say that all Chinese tubes are crap - the Black Treasure stuff out of Shuguang and the TJ / Full Music / Sophia tubes can be quite good - I believe that KR and E.A.T.'s production tends to be a lot better. It can vary by production run, however, as tube manufacturing is largely artisanal and like everything else that's hand-made, a worker has good days and bad - there can be bad quality production runs from the more prestigious manufacturers, and good quality runs from the crap manufacturers - you have to have a reputable vendor to ensure that you don't get the "runts of the litter". Why are there two different prices and two different warranties offered by some vendors for what appears to be exactly the same tube? The more expensive ones with the longer warranties tested better.