I think my 7025 Sovtech tubes (EDIT: they actually turned out to be Chinese PM 12AX7A) are ready to be replaced. I'm getting a lot of intermitant hiss and such, which I think is a good sign they're ready for the ol' in and out, to paraphrase a line from A Clockwork Orange. (ie new ones in old ones out). I'm willing to spend maybe $15-$20 a tube If I know they'll make a difference. Should I stick with the Sovtechs, or something else?