ARC Ref 5se inferior to LS28?

Exactly. Tube design isn't exactly progressing further as the manufacturers would try to have you believe.

+1 @jond 

analogluvr3

Exactly. Tube design isn't exactly progressing further as the manufacturers would try to have you believe.

That's not entirely true. For example, the KT-150 tube wasn't available when ARC released the D-79. Similarly, the 6H30 tube wasn't available when ARC introduced the SP-10 preamp.

Other components - especially capacitors - have also improved with time.

I would agree if we were discussing a comparison of the Ref 6 and Ref 5SE, or LS28 and LS27.  I've not yet seen ARC claim a new LS is better than a recently discontinued Ref series.

I've seen/heard it before Larry. Same thing happened around 5-6 years ago, when the buzz was that the LS27 was better than the Ref 3. Same marketing technique.

There are a lot of good points here but the most important one I think is simply older can be every bit as good as newer sometimes better.

@jond , +1, I agree. Interesting how when a "good" new unit comes out, there is no upgrade for around 5 years (eg. Ref 3).
However, when a new release receives luke-warm reception, and may not be a step forward, a second model follows within a couple of years (eg. Ref 2/2mk II, and Ref 5/5SE).

ARC is not alone here, I recall when Cary released the popular V12 amp. A few years later they followed it up with the V12I, which many saw as a step backward. They quickly replaced it with the V12R which most felt brought back the goodness of the original V12.

Cleeds you are talking about minor parts differences, not  different implementations/schematics.   In fact there is some differing opinion on which of the KT Tubes is best, is there not? In my opinion Tetro's or not the last word and sound quality anyway. You need to look  to the triode for ultimate fidelity.  Which ironically was developed far before the tetrode was.