Im replacing some tubes in my SF super reverb, and I noticed the previous owner had a Ruby 5u4gc rectifier, so I figured while im already at it id get a 5u4 (the original rect. tube). But whats a good option, new production and NOS? I didnt realize it would be so much more than the preamp tubes (NOS, that is). Save me a little research time and throw some TGP approved rect. suggestions at me!