It is a good idea to purchase a vintage tube pre-amp.

Since the new one are pretty expensive and what I can afford is an old one with budget of US$2000~3000. Since I don't have much knowlege on electronics, but I have authentic listening capabilities. Is it good idea to buy an old gear of tube pre amp. around 10 or 15 years such as Audio Research SP-15 or something similar (the newer one within my budget is better of course).  I would prefer a stable, long time use gear without much trouble.
True. I love the look of matching faceplates, especially ARC's and McIntosh.
Tks for your kind opinion, in order to prevent troubles, I am trying to avoid too old models. But as you know, the new models are quite expensive and one of my friend also gives the new models bad review in sound reproduction.  Such as R3, the dealer tells me that when the LED is in trouble, there is no parts for replacement........
Faust, a happy medium might be something like the LS16 as bdp24 suggested, or even a later model. I'd keep an eye out on Agon, USA Audiomart & Ebay. My only advice is be cautious about the seller's feedback and condition of the amp.
I would have said a year ago that your best choice would have been to go used (Thor, Supratek, ARC, older CJ etc.)
This could be the golden age of inexpensive preamp! The rhumba, the Line Magnetcs Micro zotl2, the new Modwright, even the Pass headphone amp integrated does some things better than their statement preamp!