I have replaced china tubes in various amps and preamps:e.g. Vox 15 (which had ruby tubes, really crap), alesis voice preamp, TLA C1 compressor (had Sovteks, which are really good, but in my second hand C1 they were old and almost gone). These work excellent, and the background noise disappears. E.g. similar spec JJs and EHXs do that too, but beside the noise gone away, I find their sound rather sterile and lifeless. Those Bugeras work really well for me.