During the Government shutdown of 2019, I built a Vacuum Tube ("Valve") Tube Amplifier using 5902 subminature tubes, and switching power supplies.
It is quite possibly one of the smallest Push-Pull tube amplifiers in the world.
While the power supplies do utilize modern semiconductor devices, the signal path is pure tube. In other words, it is not a hybrid amplifier.
It produces a few watts into 8 ohm speakers, and is suitable for it's intended purpose as a PC speaker amplifier.
The whole project is documented on the
AudioKarma Forums.