Many of us get good results with ECC189 and/or PCC189 (aka 6ES8 and 7ES8) input tubes. Well, thanks to insomnia and ebay I came across another member of the family: the YCC189 aka 5ES8, which is the same tube but with a 5.6 volt heater. I figured that was close enough to take a chance on, esp. since the tubes were dirt cheap. So I bought a sleeve of 5ES8 Raytheons and after a few hours in the UFOs I'm here to tell you they sound really good. Easily my best 4 dollar input tubes. Competitive with tubes costing 3 or 4 times the price .

They aren't as plentiful (or AFAIK available in exotic flavors like TFK or Mullard) as the 6 and 7 volt versions, but if you feel like you want a change, and/or want to try tube rolling on the cheap this might be something to consider.