I need help describing the sound of a SET to a friend in English.

1930's table radio technology! I have four of them! Best used with speakers rated for 100db @1 watt. That means something like an Altec VOTT/A7 or the slightly smaller A5.

Music comes out of a speaker, not an amplifier. If an SET is properly mated to a great speaker (high efficiency, high impedance), then you will have great music.

Like an old table top radio.

It’s like cozying up next to a warm fireplace on a brisk evening. It’s intimate, present, seductive, and memorable. 

SET amps focus on current and the first watt. The tubes add the glow and bloom to the music, and rectification and quality transformers add the push and sag to make it very involving and also softer and more pleasing to the ears.

How can "the sound of a SET" be best described sans system context and the execution/implementation/design of the SET components within that system?

Let your friend listen to a system with SET amplification and come to his/her own conclusions in comparison with his/her prior references.

A real experience versus a cognitive exercise.