Let me start by saying, right out of the box, this amp sounds amazing. After about 60 hours or so, it became even better. I had Bob Latino build the ST120 for me with all of the upgrades including the upgraded chassis.
There are 2 things that just plain stand out about this amp. The first is the outstanding bass response, its very tight, strong and digs very deep. There is no hint of sloppiness. The second, is the incredible head room, this amp has the most I have ever seen in a tube amp.
I did a side-by side with the ST120 and my dad's fully restored MC240. The ST120 easily did everything the 240 did but much, much better. Where the 240, at time, had a flabby and somewhat sloppy bass the ST120 was strong and tight. Even with the ST120 in triode mode(about 32wpc) the ST120 still had a lot more power and head room then the MC240 did.
The sound from the ST120 is very open with an excellent sound stage and some of the best imaging I have ever herd. It as if I could reach out and touch the band members. In the past, with other amps that I use in rotation, I have always used a power sub to fill in what seemed to always be missing. With the ST120, there is no need for me to use a sub as this amp digs very deep. The midrange is to die for with natural, clear high end. The amp runs quiet and is SUPER clean.
On paper, SS amps have better damping factors, THD, and S/N then most tube amps. Well the ST120 will give them all a run.

I can tell you that there are NO NEW tube amps that will come anywhere near the performance of the ST120 and it will hang with and out do amps at up to 3 times the cost.

If you are looking for a tube amp with the sound quality, build quality and BALLS, well this is it. This amp just plain gets it done and dose it very well.
And the best part, is Bob's costumer service. It is second to none. He is always there to help via phone and email. He stands behind his products and backs them with a very good warranty.

This is a very hi-end amp at an average person's price.

-Vic