Class "A" s.s. vs. tube amps

Both tubes or transistors can be Class A - it is a design choice. Tubes that have an output transformer are likely to sound the most different from s s amps (assuming a quality implementation of both and assuming no clipping)

Class A ensures no crossover distortion - it is inherently a safer design, however, a good Class AB power amplifier can be designed to run in pure Class A until around 50% power and then use Class AB in the final push pull output stages (this is both more efficient at high SPL'S where small cross over distortion is less important and good at low signal levels when crossover distortion is eliminated by Classs A operation)

Check out Chord amplifiers...

Class A refers to the operation of the output devices and is neither a tube or transistor thing- its both.

Class A makes the most heat and the least amount of power, but is also the lowest distortion. Class A amplifiers can be either single-ended or push-pull, transistor or tube, and can or may not have an output transformer.

A class A transistor amp does have a better chance of sounding like a tube amp as it will be lower distortion. A lot depends on design though- to sound like tubes you have to reduce odd-ordered harmonics, something that is challenging in the world of transistors, but not impossible.

Class A does tend to have more authority from my own listening. Ultimately I recommend that you use your ears rather than anything that you read or the like. Class A is the lowest distortion, but will be the best sounding only in concert with a lot of other design features.