The term tube amp refers to a device that uses various types of internal components to transform its signal into one that is audible and understands. These components include vacuum tubes, potentiometers, and resistors.
The term solid state amp refers to an internal circuit that utilizes a microchip to modify its signal. The majority of modern solid state amps are equipped with significant cosmetic, but not necessarily sound-changing,tube functionality.
Many people find the vintage looks and charm of older tube amps more valuable than any new feature potential might have. If you are looking at the newer models with all of the latest features, you are looking at the wrong unit. You will be disappointed if you take into account how much time and effort was spent on each feature on this unit.