Vacuum tubes are his specialty area. He's building a much larger vacuum tube computer and this is supposed to be a more mobile display version he can demo at events.

He's also done quite a few videos restoring old vacuum tube based test equipment from like HP. He does some really cool work.

Well, he described the single board version as a trainer: a way to demonstrate how the larger model works. That's likely why the address/data lines are toggle switches and the close is a button. People can setup the state then execute when ready. The much larger version is the thing you see behind him on the wall (it is a work in progress). It is also intended to go to events, but it is much harder to understand ... thus the trainer.

> Do you really need tubes for guitar distortion?

Technically no. But most professional guitarists still swear by tube driven amps. Solid state is getting better every day, but I think we're still a long way out before most guitar players give up their tube amps.

I am perfectly happy with my Line6 Helix, but a few friends still turn their noses up at it.

Solid state per se isn't getting better¹. Software simulation of tubes ("software state"?) is getting better, or has been (it may have plateaued).

Tubes are still the reference model.

All the DSP cores in a modern amp are just a cover band playing tube tones.

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1. I mean other than digital solid-state getting more highly integrated and faster, to run more complex software. The necessary analog audio paths in a DSP system aren't getting better.

Yeah, the transistors themselves aren’t changing. Just how many and how well we can throw them at the simulation.

It’s more “tube virtualization” is getting better every day.

> What's the concern with using tubes?

Reliability/longevity, power draw/dissipation, high or higher voltages.

(Speaking of the latter, I wonder what plate voltages the guy is using. I'm guessing it could be well below 100V.)