Sony 6120 Owner
I have a Sony STR 6120 and I find it to be my favorite over a couple of Yamaha receivers and Dyna SC80 s that I also use frequently. My feeling of substantiveness of the sound it produces through AR 3a s may be somewhat biased by just how massive the receiver is.
Unfortunately the right channel of the Sony blew, probably the when speaker wires shorted during an ill advised speaker location adjustment. I could not find any indication of circuit protection against output shorts, although I certainly could have missed it. Until told otherwise, I would be extra cautious about avoiding anything like a short in the output. [Yes I know that's a good idea anyway and yes I am embarrassed at my clumsiness. However, I do have lot of trouble keeping AR terminal nuts tightly fastened and wires will slip.]
I think being able to replace the output transistors should be a consideration in buying a vintage SS receiver. I don't know if there is any difference in robustness or transistor replacement availability among the 6000 and 7000 series Sonys, but I am sure someone on this forum could add something about this.
By the way, replacing the two output SD88s in the damaged channel with NTE 87s produced plenty of volume but low sound quality, so I will be seeking help on this issue.