I built my tube amplifier (along with some effects pedals) for my electric guitar at 17.

Now that I have kids, I wonder how my folks let me work with 400V of electricity and not freak out. Makes me wonder what kind of weird things my kids are going to get into.

I built my stereo at age 12, then followed it up with a (much larger) bass amplifier for my bass guitar when I was 14, and a mixer/effects box at 15. Of course they linked together, using the bass amplifier as a sub-woofer. I didn't have to deal with as high a voltage as you, just the 240V mains supply, and then the +-70V supply to the bass amp circuitry.

I think kids these days are much more likely to do something digital than build things like this from discrete components.

Indeed, and I consider that to be a huge loss. Real world skills are important skills. Just as important as digital skills but financially we seem to think otherwise.

From my experience the kid can have more understanding of what is going on than the parents, and they may not realize the risk.

400v? what that what your mains was packing?

Just a rectifier and a cap and you're there from regular household current (not safe without galvanic isolation!!). But with a simple transformer you can go way higher. Some of the end stages on tube systems I had when I was a kid would sit at 500V when idling (EL44).

Usually as soon as you see a tube with a cap on top you know you have something pretty high voltage.

No, mains runs at 230V in Europe, but as said by sibling comments, after the power transformer and rectification, HT1 (the primary high tension power bus, usually feeding the tubes in the power section) can get in the 300-500V range in some amp designs.

I knew from schematics and calculations it'd be about this high, but seeing the actual 400V value on my cheap multimeter sent shivers down my spine. Also I remember accidentally shorting the wrong wires while taking a measurement and blowing a fuse. Fun times!

Wait until you touch a live anode, that will send shivers down your spine ;)

Thermionic valves require a high voltage, because their principle of operation is accelerating electrons across a vacuum.

I wanted to build spaceships, when I was 12. I used to write to NASA, and they sent me tons of material. I used to have schematics all over the place.

It kinda fell apart, when hormones kicked in, though.

Not sure I could have done it at 15.

Same here. We were too smart to try such an impossible thing. He naïvely thought he could “just build a piano” and… well dammit he did!

In middle school, ~13 years old or so, one of my classmates set himself a goal of using shop class to make himself a guitar, wasn't half bad either. I regret that I didn't pick up the woodworking bug until later, I have made tables and bedframes and shelves now but still never got around to trying to make my own guitar. Occasionally I get jealous when I see folks with microtonal fretboards.

When I was 16 I made an electric guitar, sort of. Mostly I was interested in making a pickup from scratch. The entire guitar was literal garbage, picture wire, fridge magnet some steel dowel I cut up for the cores. The tensionera were threaded hose clamps cut open. It only had four strings so I tuned it like a ukelele. No frets though, so it sounded bad. Amd the pencil sharpener motor didn't have that much wire so I had to turn the volume way up.

I have been wondering lately what a pickup wound with wire made of lk-99 would sound like. SQUIDs for pickups...

I helped a friend make his. He got this insanely hard piece of wood for the neck and we spent a good couple of days shaping that. I'm pretty sure that if you were to look closely at that attic today you'd find that dust unchanged, that wood will never rot. It was also very heavy, a small off-cut would not float. I have no idea where he got that wood, I really should ask him because that probably makes for an interesting story but we rarely are in contact today. 42 years later and he's still into music. I wonder if he still has it.

How did the blade of your plane handle that wood?

Very badly. In fact all my normal (woodworking) tools went blunt without much progress. Eventually we settled on doing it like this: use a very thin saw to mark out the stations every 2 cm or so for depth + 1 mm, then use a belt sander (graciously borrowed to us by the father of a friend) to take it down to the marks, then endless hand sanding until it was good. It looked absolutely gorgeous when it was done. I don't remember what kind of wood it was though, the amount of dust was staggering. On one day I accidentally left the door to my attic bedroom open and everything inside was covered in dust. That beltsander did a great job though, and I don't think we'd have pulled that off without it.

If I had to do this today I'd use a metalworking mill. There is no point in trying to work wood that hard with regular wood tools, they just won't keep an edge.