You can never go wrong with Telefunken small-signal tubes- of course, they are very expensive, especially for NOS ones. Other good tubes like Mullard, Amperex Bugle Boy (both before the 1970's) and RCA black plate (1950's) should also be considered. As for SFP-1, I think it uses 6DJ8/ECC88- Siemens should be good too for this family of tubes.
