This is Audio Research's classic amplifier that established their name in the home HI-Fi industry. It's a hybrid tube/solid-state amp with A/B circuitry. I bought it because it makes guitar sound very sweet. I like guitar. I found it does very well on vocals and any instrument made of wood too -- including piano. I love it when you can hear the notes are coming from a wood box. I read this amp is a favorite of guitar players as well because it has 4, 8, and 16 ohm outputs. If they go pro, they add more VT-60's rather than get a larger amp; this way they don't lose "their sound." I've purchased an Audio Research VT-115 because I wanted more slam. I was disappointed when I received it because the new amp only added more detail -- no more slam. The lack of slam turned out to be a weakness in my preamp. One of output terminal blocks has a piece missing from one of the thin plastic fins that separate the connections. Also a trace on the mother board was repaired with a solder bridge. The main power switch has been replaced. The primary transformer was replaced by a new one from Audio Research. A few years back, I had all but the smallest of capacitors upgraded to high resolution Quricaps. In many cases, advanced technology allowed two capacitors in parallel to be replaced by one with twice the capacitance. The 6550 tubes have about half their life left. I replaced the 6922 tubes shortly after I bought the amp about 10 years ago. They seemingly last forever.