IME the best price/performance are the eastern European tubes we supply with the kits. To go very far beyond that performance-wise you start to get into spendy Telefunken, Amperex, Siemens and Mullard types. To go up appreciably from the stock tubes in terms of sonics I typically end up with Tele EF806s and an Amperex 7308 or Telefunken E88CC. They are very spendy these days. Tungsram 6922s are nice and not too spendy.
