As a first "from scratch" project, I decided I wanted to build this single 12A_7 preamp. The need came from having to drive a pair of 1959 Lafayette LA-70 KT88 monoblocks I've recently "refreshed". The circuit itself isn't overly complicated but sounds surprisingly good for what it is. It was more challenging building the 6CA4 power supply section! :) It's nice and quiet. It also allows you to roll through most of the 12A_7 family. I've found the 12AU7 is the "just right" tube, with the 12AX7 having just a bit more drive if/when you need it. The circuit mentions the cathode bypass caps as being optional, but I went ahead and installed them. I also added a "subwoofer out" jack based on another small circuit I found.

If you need a preamp and want to build one, may I suggest the 4S Preamp. It's a good little circuit that is relatively easy and inexpensive to build.