Wow thanks for the added info Hotsauce and Amandarae. My pre does not have a bias option(BEZ Q3b). I did swap for the CV 2748 mentioned and all is well. Perhaps I should stick with this tube for any replacements. It sounds good and trumps the stock chinese tube the pre came with. From my research are lots of 5AR4 subs out there from nos to current offerings. Stay tuned.