Vacuum Tubes require high voltages to work efficiently and are not for the faint hearted. They can switch several hundred million times a second, and in the 1950s they were combined with germanium diodes as the basis for many incredible computer designs.
The Tube Computer has a modern 8 bit architecture. It is designed to run a simple airship flight sim, flying around Brighton for the grandchildren, or a 64 bit Fibonacci sequence for the grown ups.