*EDIT* List of the popular tubes so far, maybe slightly biased towards tubes i own because i can't remember all the good tubes currently i'll edit in peoples impressions at a later date. In no particular order: Top 3 popular tubes: Sylvania 2 or 3 hole "Bad Boy" Foton 6N8S Ribbed for her pleasure. (50's vintage?) Westinghouse 6SN7 GT, GTA or GTB D getter The rest: MELZ 1578 See above picture for identifying a genuine MELZ 1578. PSVane 6SN7-SE KenRad VT-231 Black glass MELZ 6N8S (50's or 60's) Raytheon 6SN7 WGTA Brimar 6SN7 GT (Clear glass, orange print) Brimar 6SN7 GT (Black glass, brown base) Marconi / Osram B65 There have been some successes using adaptors, particularly the Loktal 7N7 tube which is a 6SN7 but with a Loktal base, in particular there is a Frankentube version of this which can be any make but of a particular construction. See @bcowen or @Freeflap or @Ripper2860 for advice on identifying this tube. Other adapted types: E80CC Tungsram (Neutral but sounds full, not thin, good extension top and bottom, very detailed and fast, good soundstaging) NEVZ 6N1P-VI (Mild U shape to it's signature, good extension top and bottom, good soundstaging, mids a little recessed) Orel 6N1P (More bass warmth, laid back treble and good liquidity, tubey sounding, would compliment cold clinical and fast headphones) Osram L63 (need 2 of these + adaptor) Russian version of 6C5GT (6S5S?) again need 2x with adaptor. Feel free to PM me recommendations to add to this list.