I've tried Sovtek and EH 2A3 tubes in the past, and both were incredibly disappointing, sounding just as you had described.
I would expect the Black Treasure tubes to improve a whole lot from what you heard after 30 minutes. Usually, a tube really comes into its own somewhere in the 50 - 100 hour range, but other threads on these tubes seem to mention 300 hours.
For those who are not able to swing for such an expensive tube, I've found the Shuguang 2A3B to offer much improved sound at a lower cost over the Russian variants. The Shuguang 2A3C, though a bit more than the 2A3B also is a great choice, and justifies its increased price.
I would expect the Black Treasure tubes to improve a whole lot from what you heard after 30 minutes. Usually, a tube really comes into its own somewhere in the 50 - 100 hour range, but other threads on these tubes seem to mention 300 hours.
For those who are not able to swing for such an expensive tube, I've found the Shuguang 2A3B to offer much improved sound at a lower cost over the Russian variants. The Shuguang 2A3C, though a bit more than the 2A3B also is a great choice, and justifies its increased price.