The technology pages are highly streamlined compared to the previous versions. Who really wants to learn something about the tube technology, cannot help but has to pass appropriate literature. That's why I'm holding back now with statements, I think this is a plus for the most users of this site. I want to discharge my duty and add the following:

Here I present just my insignificant opinion, I can give no guarantees and also will not be liable for damages due to the handicraft work. Please have this in mind.

Safety indications

In a tube amp dangerous voltages rule, even after the plug is pulled, because the electrolytic capacitor of the power supply can save much energy. I build up my power supplies to also quickly unload without tubes, but that is not the normal case. Therefore, a discharge of the electrolytic capacitors is ALWAYS required first! To do this, make yourself a "discharging cable".
Solder a clip to the side, then the resistor (5 k - 15 k / best a robust 2W) and tin the tip. To get something like a probe, fix a match with heat-shrink tube.

If I must admit, that I was always clumsy and actually have nothing on the hat with electricity... fingers off. Please also remember that children like to play with the toys of adults. Always unplug, discharge, screw it down... anything that needs to be done. And if you are working on something, always remember - children out!
If you build amps on your own, be aware of the VDE norm 0701-0702. I don't know the regulations for entrepreneurs, but I think that it is not so easy to distribute custom builds.