Out of the 6SN7 preamps above in your price range the deHavilland would be an excellent choice once modified. How do I know, I have repaired and modified most of them. In the deHavilland a toridal transformer replaced the original, V-Capacitors were an upgrade and Audio Note resistors were an upgrade, and tube sockets, etc. The 6SN7 tube was a cheap CBS which sounded the best in that preamp. I think you can fit a nice remote volume in there if it does not come with one.
As for the 6SN7 tubes (the deHavilland only uses one 6SN7) the NOS Tung-Sol black glass round plates were the most musical I ever heard - don't agree with the tube chart link in one of the posts above. Did not work as well in the deHavilland as in other preamps, Ken-Rads are very good, RCAs musical but soft sounding, CBS sound excellent especially as they are so cheap.Tried the CN CV-181 and with the correct bias setting they sounded very nice, pretty balanced top to bottom but overall not my favorite. Tried the Treasure WE 101D tubes and preferred the Full Music much better versus what others have said about them in the past.
Happy Listening.
As for the 6SN7 tubes (the deHavilland only uses one 6SN7) the NOS Tung-Sol black glass round plates were the most musical I ever heard - don't agree with the tube chart link in one of the posts above. Did not work as well in the deHavilland as in other preamps, Ken-Rads are very good, RCAs musical but soft sounding, CBS sound excellent especially as they are so cheap.Tried the CN CV-181 and with the correct bias setting they sounded very nice, pretty balanced top to bottom but overall not my favorite. Tried the Treasure WE 101D tubes and preferred the Full Music much better versus what others have said about them in the past.
Happy Listening.