I recently got a pair of the Treasure C181's for my Don Sachs custom octal-tube based preamp and they are an improvement over all the 50's and 60's NOS 6SL7's I have been using. They are ultra detailed against a black background. I don't know about their longevity, but they are by far the best Chinese tubes I have ever heard, clearly bettering the fabulous NOS tubes I had been using and loving. I bought a quad of them for spare. Don tried them in his own preamp and his experience mirrors mine. Check around on eBay for the best prices on them.
