Changing the tubes helps a lot. I have a Custom Vibrolux Reverb, and it hissed a lot in the beginning. I switched out all the tubes, and the hiss went down dramatically. There's still some hiss left, but that's what the CVR is known for.
Check out www.thetubestore.com
they have some helpful reviews on tubes. I changed out my tubes with the Svetlana's...my amp sounds sweet. Hope this helps.