FWIW, I found that installing SR Orange Fuses on my source components first provided the most notable improvement. As I worked my way down to the power amps, the sound continued to improve, but the biggest gains came from the source components. A power amp, after all, cannot replace musical information that is not fed to it.
Also, on the Orange, and possibly the Blue I had before them, there is a small drop of material on the outside of the tube that you should be careful not to accidentally scrape off. I expect this material has something to do with their UEF process. In all instances, the addition of the Orange Fuse was way more cost effective than attempting to upgrade the sound quality by buying a newer, more expensive component.
Also, on the Orange, and possibly the Blue I had before them, there is a small drop of material on the outside of the tube that you should be careful not to accidentally scrape off. I expect this material has something to do with their UEF process. In all instances, the addition of the Orange Fuse was way more cost effective than attempting to upgrade the sound quality by buying a newer, more expensive component.