Best Used Tube Preamp (under $750)?


I need a used tube preamp under $750, and am having trouble deciding which. I have yet to listen to these, but the price has determined these suggestions. Audio Research LS7, Sunfire Classic Tube Preamp, Rogue Audio 66, and that's all I've found so far. If you have an opinion of one of these, or a unit I haven't mentioned, PLEASE post a follow-up. Thanks all.
zorathustra
I've been on "search" myself. I heard good things about all of the pre-amps you mentioned, plus, "Audible illusions" "Anthem pre-1" and couple of others...! However, the funds are "tight" so i had to be "inventive". I found the DIY (kit)or assembled pre-amp based on famous Marantz 7. You can find more info. from "Parts Express" and Valve Audio Laboratory. The model is MP-L1S MKII. Good luck!
I love my Rogue66. Another good choice would be Sonic Frontiers SFL1 -Signature. Should be within your price range. Good Luck