I have two band new UA LA-2A . As an expensive whim, I bought two sets of GE LP 12AX7 pair + RCA 12BH7 , that were new and matched. I switched the stock tubes out for these. Was there a difference? I used a Neumann M 149 into an SPL Premium mic pre ( RACK PACK) series (to die for) which conveniently has two outputs (image) same source split (a killer parallel setup) . I was able to do a good comparison accurately between one LA2A with stock tubes and one LA2A with the GE LP. At first I felt the stock tubes sounded close. After a few minutes zoning in on things, I started hearing how these tubes have a silkier high with a more pleasing mid and fuller lows. The stock LA2A sounded just a bit edgy compared. Not quite as hifi. Don't get me wrong though, if I hadn't switched these out, I'd still be in love and should and when these new tubes die, both my stocks LA2A's are to die for. I have backups tubes now but oo la la... these new tubes are staying! Comparing both LA-2A's after both sets installed, sound so close I trust they were matched very well. Thank you Christian from ProAudioTubes. You were extremely helpful and very interesting! I will be calling you for more tubes. I'm happy to report, tubes do make a difference and these GE long-plate 12AX7 on the output with the RCA 12BH7 sound great! They are also very quiet and not even broken in.