• 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.

Recommend first DIY project - phono preamp

Bottlehead are very easy. You can even do it if you cannot read schematics. I have built the phono and it works well. The photos will guide you through and you can test it with a multimeter. They sound fine too. I have built a number of the Bottlhead kits.
I will qualify my statements with the fact that I have known Dan Schmalle (head Bottlehead) for about 25 years. His kits work. Get an optivisor if you are over 40 and save a lot of grief over dry solder joints due to presbyopia.