I’ve never had an amp I felt that way about, but: I would keep and design around an amplifier if it had high input impedance, several taps to accommodate different output impedances, at least average wattage, and good gain. If class A/B, I want to know at what point it leaves class A. I also want to know how much it weighs, a heavy amp makes me think lots of effort has been put into the power supply. Oh, I would want the ps shielded from other parts of amp.