No need to buy a vintage tube preamp when Don Sach's is offering a SOTA tube preamp, based on the venerable 6SN7 octal tubes, for around $2K, plus/minus. I got one of his prototypes and have had him incorporate his upgrades to his current offering, and it is a stunningly fine preamp. Google Don Sachs and look at this line stage. It is by far the best preamp I have ever heard in my system by far and I have had more vintage tube preamps that I can recall. I reckon I could not improve on its performance for under ~$10K. Good luck.
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.