Harman/Kardon Receiver

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,

Xavier

xaviercg,
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.
Avondale

Love my 430 powering ADS L1290 mkii speakers. Amazing sound. I used to have a 930, too, but it went belly up.