I previiously had an Audio Research LS26 which sounded superb. Plus it is both single ended and ballanced. Should be able to get a good used one for around $3000. Can not do better for the money.
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.