I was always a JJ KT88 fan, and felt they produced the best sounding current production variant.
However, when Shuguang introduced their Black Treasure, they raised the bar much higher than the JJ, which produce a hard, glassy sound in comparison. The Black Treasure put forth better transparency along with the liquidity and musicality. Over time, like most Shuguang tubes, they’ve also proven rugged as well, and easily best the JJ and the other European tubes in that area, as well.
The Psvane KT88 then came along, and sounded better still than the Shuguang Black Treasure. But after their initial launch into the market, they supposedly moved from the Shuguang to Guiguang factories, and longevity nosedived. Presumably, they’ve corrected that, but I’ve not gotten near them in a while, as I don’t run KT88. When people ask me, all things considered, I recommend the Shuguang Black Treasure.
Regarding the blue and red glass JJ tubes, back around Y2K, someone told me the blue glass run 2 degree C cooler than the clear glass. The red glass run 2 degree C hotter than the clear glass. Over time, I heard others repeat that. As I once imported JJ tubes, the factory told me that was hogwash, so it was purely an urban legend. I always loved the blue glass, and personally run their E34L. But after it’s become ubiquitous, I sort of like the uniqueness of the red glass, which you don't really see in North America for whatever reason. The previous Tesla / Teslovak tubes that evolved into JJ had a much superior color on the tubes
