Which NOS to use on Audio Research pre amp?

Use 4 Siemens in my LS-15. With infini cap upgrade and try DIY power cables. Now I am comparing this one to BAT VK30, which is pricer using 6 Jan Philip tubes now. I prefer LS-15's middle frequency over BAT. BAT has better bass control than LS-15. Siemens improve the high and low end, IMO.
Now, plan to keep LS-15 and sell BAT (both are very nice preamp's). I did not have 6 Siemens to put in BAT for a more complete comparison. But I am pretty happy the way LS-15's sound now and will keep it as now for some time.

Thank you everyone for your opinion. I will give the NOS tubes a try and swap out the Sovtek's which I think is making the sound bright, everything else seems to be okay, but I with the right NOS tubes it will improve.

I currently own an LS5 MKIII and I have tried the original Sovtecs and Telefunken E88CC (6922).

In my set up, I found that the Sovtecs put the soundstage at the front of the speakers and I was surprised that the instruments were very sharp and focused. I was expecting less than this, to be honest.

The Telefunkens, on the other hand, added more air and depth. This put the soundstage between my back wall and the speaker.

Note also that I also using an ARC VT130se amp that was modified by Great Northern Sound, using GE 6550 power tubes and Siemens 7308 input tubes along with Coincident Super Eclipse speakers.

Tube rolling, although frustrating at times, makes a huge difference, in my opinion.

Steve

Gold Aero if you could get them.

I do remember back a few years I upgraded a ARC preamp with Orange Label Amperex which was a great improvement.Amperex is a great NOS tube to start with and usually is not too expensive. Generaly each different manufacturers ( nos ) tubes have a unique sound so its important to know what your looking for,which will help steer you to the right direction. good luck

I have an SP10II - i use 6h23's in the line stage and Seimans in the Phono Stage. When i get a chance i'm going to try some EI elite 6dj8's in the line stage - i've used them as drivers in an amp and like them a lot in that application.

I had a LS7, which is not even in the league your Reference One is, but I have rolled some tubes with various results. I have tried the factory-supplied tubes, with dampers, Amperex PQ’s and Amperex Bugle Boy’s. The factory tubes were OK, the soundstage was wide, but not real focused. It seemed a little muffled to me, especially comparing to the other tubes. The PQ’s were really quite an upgrade. The soundstage became very focused and the bass extension was noticeable. I tried the BB’s, and I felt they had the best feeling of depth, I ended up keeping them. My system has some lacking points, especially the speakers. I also don’t have any room treatments yet. The one tweak that had some effect on the BB’s was brass tube dampers from Mapleshade. It seemed to give the center stage better focus and better definition of the instruments.

Tube rolling is fun and there is definitely a difference between tubes, even within the same brand and model. Just pick a batch and start trying. Other have had good luck with Telefunken and Siemen tubes, but I haven’t tried them yet. I hope others will post on this, because there is a world of knowledge by some of these folks. Hope this helps a little.