New tubes or new preamp?

I have an ARC LS15, and am considering either a set of NOS Amperex tubes, or selling it and getting a new preamp, such as an ARC LS27, or a Modwright LS 38.5.
As I'm unable to compare , what would you advise?.Will NOS tubes give me a preamp that compares with todays current ones, or is it a waste of money?
Buy 4 tubes or a preamp that costs more than double the price of your current preamp is an amusing question. I think NOS tubes have become extremely overrated. If you want your LS-15 to sound its best you should send it back to ARC for a complete checkup and fitted with tubes selected by ARC. If you want an upgrade buy the LS-27.

I cannot comment on Modwright products.
I got a set of tubes from ARC and they were so microphonjc I Sent them back. Really want to know if spending money on an older per is worth it versus a new one.
There's more to a preamp than just the tubes. For me, the preamp is the most important piece in the system. (Providing you don't mess up matching your other components.) Get the LS-27. Its a big upgrade.
A set of good old stock tubes will change the presentation of your LS-15. I have tubed rolled a few LS-15 and LS-25 WITH VERY NICE RESULTS but if it is a major improvement you seek you should consider moving up to a better preamp of which there are many to look at.
PrimeOne Media
The basic circuit of an older preamp is less sophisticated then a newer one.
If you like the sound of your current setup then buy the tubes. If you want more, then buy the new preamp.
Brrgrr, So far, I haven’t heard an amplifier that couldn’t be improved by upgrading the stock tubes. So, that might be enough for you; it frequently was for me - at least until I found and could afford a clearly superior amplifier. As a rule, I consider it highly advisable to seek out the right tube set for any amplifier.

Tube rolling can be chancy, expensive and frustrating; all of which become worthwhile once you find the right set. I tend to think of the manufacturer supplied tubes as a sort of blind date chosen for consensus appeal. I appreciate the effort, but only I am listening to my music with my system in my room.
Good advice all...I've recently upgrades my speakers to Magnepan 3.7's, and bought a Magtech amp. Still not getting the sweet sound I'd like. As I tried new tubes from ARC and still wasn't where I'd like to be, thought either a tube upgrade or a new tube pre might be the way to go..I can't audition, due to the fact there are no dealers anywhere near, so I"m looking for some guidance for those here who have listened to a lot of gear I can't.

I'm prepared to spend some money if the return is there, but want to make sure the difference in expense is worth it....
Thanks for your input...
When I had the LS15 I researched getting different tubes and was told by a few reputable dealers that the LS15 was not a good candidate for tube rolling, that the benefits would be minimal.
There were two versions of the LS15. If you have the older version (most easily identified as it has a captive power cord) then the cap and power supply upgrade by ARC is a very cost effective improvement.

After reading your 2nd post, I don't know if you will get the results you want by getting a new preamp. It looks like you want something to deal with your 3.7's not having a "sweet" type of sound. Getting an LS27 most likely won't help. If anything, its a more transparent preamp and will further enhance what you don't like about your speakers.

Given that, I think you have 2 choices. The first choice is to buy equipment in an effort to cover up what you don't like about your speakers. Its a very tempting option, but almost never works. You'll just end up spending a lot of money. The 2nd choice is recognize that you may have bought a pair of speakers that are not for you. If thats the case, deal with the issue directly and get a different pair of speakers. For me, personally, that would be the way to go. Deal with the problem and be done with it.
"Still not getting the sweet sound I prefer"..........If by 'sweet' you mean rolled highs or midrange warmth, I'd agree with Zd542. It is very hard to change the fundamental sound of speakers by changing amps etc. That said, however, IMHO the electronic's you seem drawn to are not noted for their warmth. Detail, transparency, speed, etc, for sure. Warmth, not so much.

FWIW I've never thought that panel speakers matched to SS amps, etc, were a match made in heaven for folks who want warmth/sweetness. But if you think a tubed pre-amp will do it look for something that is noted for it's warmth/sweetness
not its transparency etc. ARC would not be my first choice buy some margin, neither would a Modwright, fine though they may be.
I am an inveterate tube roller who can tell you that in some cases of ARC gear, - tube rolling is not useful. I own a highly modded ARC SP6B which uses 6 12AX7s. It was very difficult to tame the glare I sometimes got using this pre. I had all sorts of tubes to roll none fixed the problem. In the end I just put in some good tubes of no special merit and gave up.
I don't know if that is the case with your ARC pre but even ARC would tell you which tubes were likely to change the sound and which did not.
You can buy a tubed pre that may be to your liking, but I have to agree with some others and say, that more ARC gear is not a going to cure your system's ills. I can't comment on the other brands you mentioned but you may want to check out 6SN7 based pre amps from Cary, such as the SLP-05. You can put a whole host of different tube brands and vintages in that pre.
I have had that preamp and the sound is dated even with vintage tubes Good for the money but not a Ref 3 or 5. Sell and replace it if you want a bigger step forward. Tube rolling is way overrated. Tubes only do so much. Jallen
Dump the ARC pre and get one that is more lively. I just went through this with a ARC SP-9 MarkIII. A pre-amp change absolutely transformed my system.
Russ69, What did you get to replace it?
Jallen that was very dismissive, listen to what the OP wants. ARC gear is "High Definition" to some this accuracy is what it is all about to others not so much. There is room in this world for more than one preference. I went to great lengths to illustrate that tubes don't allways change the sound.
"07-01-13: Brrgrr
Russ69, What did you get to replace it?"

I'm embarrassed to say that I put a NAD C162 pre-amp into this system (not my main system). It's my back-up pre-amp. The NAD is full sounding with good bass. It kind of funny because I have a Mac MC402 amp in this system (my most expensive component). Anyway, I have had the AR pre-amp in and out of many systems and it is very detailed but in the wrong system it just doesn't have any bounce. You system sounds like it has the same problem. Maybe you can borrow another pre-amp and see if that does the trick.
"I put a NAD C162 pre-amp into this system (not my main system). It's my back-up pre-amp. The NAD is full sounding with good bass."

Did you leave the SP-9MKIII powered on all the time? If you did not leave it powered on you never heard it. So now you think the OP should dump his Audio Research preamp and get an NAD?

BTW, AR is Acoustic Research.
Rrog says: "Did you leave the SP-9MKIII powered on all the time? If you did not leave it powered on you never heard it. So now you think the OP should dump his Audio Research preamp and get an NAD?"

I have had the ARC SP-9MKIII in 3 of my systems and listened to it in 2 of my brothers reference systems. I'm pretty familiar with how it sounds. I also have a ARC LS-2 and a Cary SLP-98 to compare it too. Oh and I guess the old NAD and another pre. Anyway, in the wrong system it can sound a little dry. I'm thinking that is the OPs problem.
I never recommended the NAD, I told him to borrow a different pre-amp and try it out. The synergy with the ARC pre-amp wasn't there in my system, maybe your system is not like mine and you have different results. I'm just passing on my results, if you don't find that useful, for your system, then maybe we both learned something.

Thanx, Russ
I've been running direct from my Oppo 105 for a bit, as I returned the tubes ARC sent , and just have an old set of Sovteks that are not good, to say the least. Will have to get a decent set of tubes so I can sell the LS15 in good conscience, and give it a listen at the same time....speakers are starting to settle in and the sound has improved recently...just need to decide on a preamp....will probably try to get a used one and , if it doesn't do the tick, resell t and try something else...the joys of no decent local dealers!..