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.
The list of champions competing with today's high-end monsters:

Pioneer SX980, SX1280,
Sansui AU 717, H.H.Scott Stereomaster 

to name just few out of many...

i have a 430.   it sounds good because they knew how to make a good receiver back then.   and more power from the 730 proves more power dosent mean better sound.  last i saw, the 430's were going for $200 and up on the bay.  
The HK 430 is a bit of an anomaly.  Not all receivers of that vintage sound so good.  Prevalent use of discrete componentry, oversized power supply for the design and engineers who actually listened to the product probably explains most of it.  

I owned one, garage sale purchase for $20, took it home and gave it the classic Deoxit treatment.  Ran it with a Nak CD player and a pair if Snell K monitors.  Also ran Rogers LS3/5As, Spica TC 50s and various other monitors with satisfaction.  A ridiculous product for the investment.
i'm also a big fan of the hk x30 series and still own a 730 and 330, having also owned the 930 and 430 at various points. i've read that unlike everyone else, hk used very little negative feedback in their designs, which resulted in less interface and transient interface distortion (whatever those may be), which are supposed to much more audible than THD. i'm not sure about the tech stuff, but to my ears the hk always sounded more lifelike than the sansui, pioneer etc. of the same era.
A classic for sure.

Here's a picture showing the output transistors for the 430.


IMHO, that is one reason for the quality sound. I have had experience with many vintage units, and the ones using this type of output transistor always sound very good. BTW, same type of output transistor as the NAD 3020.

Thanks to all for you kind responses.  I am going to try to obtain an Owner's Manual for the unit. 
If I'm not mistaken, the 430 was part of their lineup that used separate power transformers for each channel. So its a dual-mono design in a single chassis. That is a good portion of why it does what it does.
the 430 had a reputation as the best of that line, even better than the higher up models...
You have the best kept secret in audio!
Some history, the 430 was discovered
by Robert Fulton of FMI back in the mid
70's he preferred it to his Levinson ML1
He would it believe or not to drive his 
Premier 250lbs. speakers.
Would use his Bravura preamp., and tap into the amp. section of the 430
for those 30 watts.
Now naturally, the HK didn't have the
power to drive his speakers to full range especially when playing symphonic music but when playing small ensembles, vocals, jazz and chamber music it 's like the musicians
were in the room simply magical. 
Even by today's standards the HK430
is a keeper.
Incidentally, Bob was the engineer that 
pointed out to the audio industry
that speaker cable is a component,
when everyone was using zip cord wire.
Bob was an old school engineer new 
what music is suppose to sound like.

Well I hope this helps,

 Best regards and happy listening,


Many thanks for your kind and informative response.  I admired the work of Ropert Fulton and have a pair of his Premier speakers which I have had for 30 years and still consider it one of the very best speakers ever.  I never imagined that he knew about the HK 430 or that it could be used to drive the Premiers!
Best wishes.
Love my 430 powering ADS L1290 mkii speakers. Amazing sound. I used to have a 930, too, but it went belly up.