Audio Research Reference 5 Preamp

What doe ARC know now that they did not know then to make the Ref 5 a marked improvement of the Ref 3? Is it improved capacitors and resistors or power supplies? A totally different circuit design that was not conceivable then? I would have thought that there best thinking would have gone into the product five years ago, what has changed? Is there really a new state-of-the-art in preamp design, or have the fundamentals been in place for a long time already in terms of circuit design and improvements will come when there are truly better passive parts available. I'm not sure what has changed in five years.

I've hard "negative" comments about 6H30, many folks thinking that is where ARC went wrong, right after your LS-25MKI. So I wonder if the "improved" implementation of 6H30 is starting to sound as good as the great 6922 preamps, but maybe with some other advantages (whatever they may be) of the 6H30. What you say makes some sense though, it proabably does take time evolve with a tube that was essentially new to the market.