Hi here ! I'ld like to change the tube of my Fafner (blue Fafner), but i dut no much about 12ax7... what will be the difference (sound and quality) between those once : - Groove Tubes 12ax7 C or 12ax7 M - Sovtek 12ax7 LP (i need a LP or a LPS for my amp ?) - Electro Harmonix 12ax7 EH - JJ 12ax7 - Ei 12ax7 - Svetlana 12ax7 (what is the difference between "c" or "s" label ?) I do like GT, but i don't know why... the name ?? the brand logo ? billy sheehan ?