I owned the ARC Ref 600 Mk lll (predecessor to the 610), Indeed they were great but the heat given off by 31 tubes per amp (62 in all) was unbearable even after I installed a 3rd dedicated AC for m listening room. I was going to buy the 610's but did an about face and went with the Lamm ML 2.1 at 18 wpc. The best amp I have ever owned and would never change