As far as new tubes go generally speaking Tesla's and Svetlana are the comapanies to go with.But because (driver)pre-amp tubes last so much longer it does make sense to invest in NOS.You might get some strong used tubes and compare them to others.If you went with say french Mazda's they would be cheaper than Tele's,Siemans,or Mullards.But this can be a fun thing to try and you wouldn't lose that much by buying and re-selling the ones that aren't used.
