• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My first tube preamp

The original Aikido Preamp design was here:
https://www.tubecad.com/2004/blog0011.htm

The circuit was popularized by John Broskie.
Hi blog is Tube CAD Journal
https://www.tubecad.com/

The Aikido Preamp is going to have quite a bit of gain, perhaps 10x (20dB).

If you want something that adds no gain but still offers some (albeit minor) benefit, you could try a simple cathode follower as a preamp. Something like this perhaps: https://www.diyaudio.com/community/...r-tube-buffer-using-6n6p.169150/#post-2228200
That thread is from 2010.

Simple Tube Preamp threads:
https://www.diyaudio.com/community/threads/6v6-line-preamp.102352/ (from 2007)
https://www.diyaudio.com/community/...the-12b4-better-than-the-grounded-grid.68267/ (from 2005)

As you can see, this topic has come up before.

There are many other possibilities, and many more threads.