That issue of Stereophile was my initiation into audiophiledom, and the ARC SP-3 my first serious pre-amp. My dearly departed pal Brooks Berdan sold ARC when he was at GNP in Pasadena, but by the time he opened his own shop (Brooks Berdan Ltd.) in nearby Monrovia, ARC designs had become hybrids, rather than purely tube. Brooks kept his tubed SP-10, finding the hybrid SP-11 somewhat "dry and white", as he put it. At that time I had an SP-6b that I bought from Steve McCormick, which I ended up selling to Brooks. Both the SP3 and SP-6, as well as the SP-10, are the classic ARC purely tube pre-amps.
Brooks became a dealer for Jadis, VTL, and Music Reference, all still making pure-tube electronics. He took in a lot of ARC from people who liked the pure tube sound of those companies products more than the hybrid sound of ARC. But Bill Johnson and Rich Larsen kept working at making their hybrid circuits sound more tubey and less solid state, and eventually got rid of the ss nasties that Brooks and some others (Harry Pearson at TAS) found objectionable. That was years ago, and ARC is still at the top of the heap. They are unquestionably the most influential high-end company of them all, but they did put out the occasional turkey! I agree with the comments above, that the way to buy ARC is used. But if you buy a power amp, you had better have a dealer who does repair work nearby. If you have an output tube go bad, you're gonna need him!