I was wondering about this a while ago. 

I believe the answer is - the units with "Ultimate" written in red were more limited edition with even higher-quality parts.

For example, the Luxman L-540 has an industrial-grade IE power transformer. Very similar to what companies like Nissyo produce. (for converting 120 or 110 v to 100v). These are often better than torodial power transformers and may last / funtion properly up to 20 years plus.

The older models under alpine/luxman for the most part were not very impressive. Especially the build quality. When they wanted to become a more premium brand, the vintage VU meters, heavy casework, and large custom heatsinks were proably a copied concept from flagship units sold by Sony and Pioneer, who were doing extremely well in terms of number of units sold vs all other Japanese brands at the time.

Indeed I was wondering if they had higher quality parts and better parts matching, including for all the tubes including the 50CA10 output tubes.

One other characteristic feature for the Ultimate, at least for the lx-38 integrated amp and cl-36 preamp was the lacquered wood cabinet.  It is the nicest cabinet I have ever seen on an audio component.

I believe these were manufactured in the period just before Alpine purchased Luxman.  Very difficult to get more information.  I’ve reached out to some Luxman experts with no success.

The best vintage solid state amp and preamp Luxman made, in my opinion is when Luxman was under the ownership of Alpine/Luxman see below. FWIW: I bought brand new in 1977 two Luxman B-12 monoblock amps and a Luxman C-12 preamp. They were the Laboratory Standard Series before the Alpine buy out. The better line at the time was the Laboratory Reference Series but my budget would not allow for it.

Mike

Luxman twin-monolithic preamplifier C-05 & pure Class A power amplifier M-05:

( $7000 )