It may seem like I joke around a little bit in other places on this website, but I don’t joke around about safety.
High voltage will f@!#ing kill you if you give it the chance. Don’t give it the chance. Don’t operate on equipment if you don’t understand it. Don’t poke around the inside of a powered up amplifier. Always check that all power supply capacitors are discharged before poking around an amplifier that is powered down. Don’t fart around with crusty-ass frayed wires. Always overrate voltage and wattage in the parts you use. Don’t use those f$%@ing three prong to two prong power adapters on your shit. Always use a fuse. If you smell burning or see smoke, turn the equipment off (safely) and do not turn it back on until you know what went wrong. Always check the insulation rating of the wire you use.
Always work with only one hand, in order to avoid creating a circuit across your chest, when you aren’t sure if a circuit contains dangerous voltages (including in the supply caps). Always wear shoes with rubber soles when working on tube equipment. Always wear safety glasses.
Make sure anything you build with tubes gets proper ventilation and breathing room.
This list is not complete and your safety is your own responsibility. I’ll keep adding to this list as I think up other dumb things that people probably try to do.
Here are some pictures of tube shit that blew up and ruined someone’s day: