Agree with every one. Telefunkens have a special magic in the JP-200. Have had the JP-200MC since 1995 and had it updated at the factory in 2007. Still believe it is the best sounding preamp I have ever owned or heard. The best tubes have always been Telefunkens. Mine has all Telefunken 803S. Also agree you should avoid any mods to Jadis equipment. Had one done on the JP-200 and it took away everything that makes the JP-200 the wonder it is. Recently heard the new ARC Reference 40th Anniversary pre and was struck by how much it reminded me of the JP-200.
The 5751 (preferably RCA or Sylvania black plates) substitutes beautifully in the pre for the 12AX7/ECC83. Has slightly less gain but add a sense of ease to the sound. Use it in place of the ECC83 in my JA-80s and prefer it to the ECC83. While on the JA-80, for the best sound of all substitute a 12SN7 for the ECC82/12AU7 (you will need an adapter). The 12SN7 is far more linear than the 12AU7. You can also substitute the 12AX7 for a 12SL7 (again you need an adapter). The difference is not quite as dramatic as the 12AX7 is more linear than the 12AU7, but the sound stage becomes wider and deeper. Recommend it.
The 5751 (preferably RCA or Sylvania black plates) substitutes beautifully in the pre for the 12AX7/ECC83. Has slightly less gain but add a sense of ease to the sound. Use it in place of the ECC83 in my JA-80s and prefer it to the ECC83. While on the JA-80, for the best sound of all substitute a 12SN7 for the ECC82/12AU7 (you will need an adapter). The 12SN7 is far more linear than the 12AU7. You can also substitute the 12AX7 for a 12SL7 (again you need an adapter). The difference is not quite as dramatic as the 12AX7 is more linear than the 12AU7, but the sound stage becomes wider and deeper. Recommend it.