Never had a 2000S, but I do have a 200S I use every week. I got Svetlana KT88's for it. The Svets sound really hi-fi in my 200S. If you want to use KT88's (four of 'em) in your 2000S, first get either two matched pair or a matched quad of KT88 tubes of your choice. I would avoid Chinese tubes.
To set the bias voltage, the following has worked well for me:
Remove the chassis from the cabinet. Plug in the new tubes, turn on the amp and allow it to warm up for a few minutes. If you have a schematic and know the nominal (-) bias voltage between grid and ground, measure it. With a solid-state rectifier the bias voltage will be more negative than with the tubes rectifier. Move the bias voltage toward zero until the plates start to glow dully (the room must be dark). Now, increase the negative bias voltage until the plates are plain black (no red glow). Read the voltage and record it. As long as the plates don't glow at all, you are OK. The biggest sound and good tube life comes with the bias set such that the output tube plates don't glow, combined with the lowest bias voltage (grid to ground) consistant with the plates not glowing anywhere. Do the final adjustment in a completely dark room. Fat sound, and you don't wreck the tubes. At least that's how I do it. It has worked well for me. If your 2000S still has the dual rectifier tubes, you may want to contact Gerald Weber at Kendrick Amps for better advise, although the above should work OK with the pair of rectifier tubes.
