Warming up the ARC LS2B

I would like to warm up the sound (add a little more tube sound) to the LS2B. Anyone know what tube works well for this?
First of all, are you leaving your LS-2B on all of the time?
Years ago I did quite a bit of tube rolling with an LS2B, along with a friend who also owned one. The warmest of the tubes we tried, if I recall correctly, was a Mullard, while the German variants (Siemens and Tele's) ran very linear and more on the neutral side. Hope that helps. Also, my LS2B had been modded by GNSC - in direct comparison both of us could tell the differences blind and that mod occurred to both of us as worth the price at the time. I don't know what they're charging now. Improvements were not in warmth though, but more in resolution and soundstaging.
I agree with Jax. The Mullards are still one of my favorite tubes. I also like the Amperex Bugle Boys.
Put some brass Edensound Bearpaw footers underneath..More relaxed and warmer with better bass impact...
Change out the diodes to Hexfreds or Schottkys.
Change the coupling caps to something that has oil like Jensens.
If you are driving one one power amp of input impedance 100kOhms or higher, disable the FET follower stage.
The LS2B is not known for warmth and musicality in the first place.
rolling tubes only introduce marginal changes on a hybrid preamp.
you can put in a lot of $$ buying those pinch waist Amperex PQs and what you get is your imagination tell you that its warmer.
Doesn't someone make a tubed buffer "black box" that is inserted
between the source and preamp?

Google yielded:

Pacific Valve Yaqin CD-1 ($200)
and the ZBOX from Decware ($449).

This might help.
I had an LS2B and several other ARC preamps from this era.
If you don't like its sound (I didn't), look for an SP8, SP10, CJ preamp, or Quicksilver...

The worst sound I ever got from my ARC CL60 was with the LS2.
I have had the LS2B, and liked it. It sang best with a Mullard. Also, listen to a Amperex BB or PQ. They are nice if you get a good one.
Audio Research hybrid preamps need about 3 days to start sounding their best. If you thought your preamp would warm up in 30 minutes because it has a tube you are mistaken. I have known many audiophiles who never knew this, but thought their system was sounding better by the end of the evening.

The tube in these hybrid preamps has a very long life and if you leave your preamp on 24/7 you will only need to replace the tube once per year. This is a small price to pay for the improvement in sound.

If you don't leave it on you will never know what you preamp is capable of.

Do this before changing tubes. You may be satisfied with the sound.
The LS2B is not known for warmth and musicality in the first place.

I'll amend my original response, with some agreement with the above statement. I always found the LS2B to be rather cool and detached - and yearned to find warmth there as well. Though the Mullard is a fine tube, and did impart some sense of "warmth", it was only a bandaid - I actually preferred the pre with the more linear/neutral Siemens CCa tube for greater resolution I believe, though thought the Mullard was very nice as well (consistently my second choice). I believe I had the LS2B for a year or two, having tried pairing it with several different amps, and it's one of those components I really don't miss much or remember with much fondness, especially having a whole lot of experience with much better preamps. I used to keep mine on 24/7 per the suggestion by Rrog. I really can't recall it making a night and day difference, but then... it was a long time ago. BTW, I would certainly not consider the tubes being discussed as inexpensive. The Euro 9-pin varietals that are the cream of the crop of E88CC's range from $130 up to the $300+ range per tube from a reputable seller. Fortunately you only need one. Ultimately I'd suggest that if you are highly unsatisfied with the foundational sound signature of that preamp, which I would classify as cool and analytical, sell it and buy something that may suit your tastes better as the improvements, at least in my experience, are not enough to change the basic signature of the pre.