Most of these are hybrid amps which start with a solid state circuit and just add a tube for looks and possible "tube coloration".
The benefit of real all-tube amps is that tubes are way more linear than transistors and require much less corrective circuitry, which will appeal to audio purists.
I don't have personal experience with these, but check out APPJ 1502A, Darkvoice 336SE, Little Dot MKii, FX Audio Tube-P1.
Or if you're seriously into DIY you can get one of the single ended class A 6N2+6P1 integrated amps, about $140 with shipping from China. If you add a headphone jack you need to make sure to add a parallel 8 ohm 10 watt resistor so that the amp sees the expected load. You'll also need a drill bit suitable for drilling the steel enclosure: