Harman/Kardon Receiver

Sometime ago I acquired for $75.00 a Harman/Kardon 430 receiver in exellent condition (all original) for a small bedroom system. After having it serviced, I have recently begun to use it, and I am astonished at how musical it sounds.  Associated equipment include Snell J IV speakers and a Cary 308-T cd player, interconnects are by The Cord Company and speaker cable is by NAIM.  The sound is so musical and satisfying that I can listen to it all day without any listener fatigue at all.  My question is if some of you experts on receivers could tell me why it sounds so good? I have no information at all about this receiver and would appreciate any insights the Audiogon family could provide.
For what it is worth, in the past I heard a Harman/Kardon 730 receiver and did not find it nearly as involving musically.
Thanks to all in advance and cheers.
Avondale