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

SET aficionados tend to look down on SETs that (1) use many output tubes in parallel and/or (2) use triode connected pentodes or tetrodes. The Golden Tube amp is guilty on both counts.

If you’re asking me, I have my own audio passions, convictions, and biases, and they don’t include SET-based systems. Although I do respect the concepts, I am not knowledgeable when it comes to the current market.

I once listened for an afternoon to two of the very expensive SET amplifiers made by Audio Note, original Kondo designs from Japan, not the UK imitations.  One was the Ongaku (around $70,000) the other was a Kegon (more than $100K) up- and downstream components were exactly the same, same program material too. (Speakers were also very expensive Audio Note, made for these amplifiers to drive.)  Both amplifiers sounded very good, but they were also very noticeably different sounding, one vs the other.  I concluded from this demo that the best (or these most expensive) SET amplifiers represent a purchase that one must make with the consciousness that you are buying colorations that you had better like. So, you are not doing your friend a service to just recommend an SET amplifier unless you are intimately familiar with what he likes and that his speakers are suitable.  Into the wrong speaker, any SET will sound like crap.

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.