Do new NOS tubes need break-in/running-in?

I have bought a few Mullard ECC88 NOS tubes and to my lousy ears, found no sonic differences between these and my current Amperex ECC88. Quads were used in my ARC LS-16 preamp.

If there is such a thing as break-in for tubes, will NOS tubes sound any different and/or better after break-in? If break-in is required for NOS tubes, what is the rough estimate for break-in period?

I have a strong feeling that I won't be able to get significant sound improvements/differences after prolonged listening hours. Maybe my preamp is not too susceptible to different tubes?

Any opinions or advice would be much appreciated.
Break in.....yes for everything.
Should improve sound.
yes, 5 to six hours...before doing a post like this in future suggest you check the's been beaten to death (as have many generic topics)
I not sure Mullards are really any better than Amperex. It would depend on specific models. The tubes would need a moderate amount of run-in time say 10-30 hours. Yes, some designs are not sensitive to tube rolling. I'm not sure if your Audio Research is one of those designs.

BTW, you setup and house looks fantastic.
No changes after 5-10 hours of use.
Thanks for the responses. Usually I check the archives before posting but this time I'm little impatient I guess.

I've owned Sonic Frontiers Line 1 and find it to be not sensitive to tube rolling at all. I will try to run-in the tubes longer and hopefully the ARC will not exhibit this similiar trait. Well Onhwy61, your system looks great too.
Tubes can take up to 100 hours to break in, there is no set time so just wait it out.The rectifier tubes in my Art Audio Diavolo took 200 hours. There where also many Mullard tubes labeled with the Amperex label, so they may be the same tubes. You definetely will hear a difference between a Mullard and a Amperex.If you do not,they might be the same tubes. To answer the question regarding the Audio Research LS-16, yes,the tubes make a large difference.I preferred the Mullards, but that is my taste.
I have rolled small signal tubes quite a bit, especially 6DJ8-E88CC-6922-E188CC-7308 types, and found that a tube's "flavor" shows more or less immediately, in minutes, but the flavor usually develops, so to speak, over the next 5-6 hours; sometimes more, but I can't remember a small signal tube that's changed much after 12 hours.

I wonder if the process with tubes is really a "break in" or a thorough "warm up." Tubes heat to operating specs quickly when they are used in a component, but NOS tubes have been on the shelf for quite a while, so I wonder if they're really just waking up, as it were. The time may vary with whether the piece is designed to be easy on tubes or not. 'Not sure where your ARC piece falls in that continuum. The difference between break-in and warm up may be semantic, but maybe not. With tubes, I've never heard the kind of fundamental change that I've heard with other components. When I first played my Virgo 3s, for example, I thought I had made a very expensive mistake, but one morning I woke up and they sounded great. Similarly, anything I've owned with Blackgates hasn't shown is most developed mellifluousness until it hits the 200 hour mark -- and then some. For me, at least, I've never heard that kind of changes in tubes. Again, ymmv.

But Majicjazz may have hit the nail on the head. Tubes branded Mullard or Amperex may actually have been made at the same factory. The way to tell is by looking at the second line of the etched codes on the side of the tube, near the bottom. If the second line begins with an asterisk (*), then it was made at the Amperex factory in Hicksville, NY. If it starts with a sideways triangle (almost like a delta symbol), then it was made at the Philips factory in Heerlen, Holland. If it starts with a B, then it's from the Mullard factory in Blackburn, UK. It's very common for tubes branded Mullard or Amperex to have been made at the Heerlen factory. If your tubes sound the same, that may be the reason. My .02, as they say. Hope this helps.
I am little relieved after reading the post by Majicjazz. At least now I know the ARC preamp will be quite receptive towards tube rolling.

Thanks for the comprehensive post Jbaxley. I will see if I have time to check on the etched codes on the Mullards this weekend as it requires a bit of work to unplug everything and get the piece out from the shelf. Hopefully they are not the same Amperex tubes as I paid quite a bit for the NOS.
It is a P.I.T.A. to open the preamp, but while you're at it, you may find it interesting to try to decipher all of the codes. So here's how to read the rest of the codes. In the second row, there are usually 4 characters, which signify as follows, in this order: [factory code][year of production][month][week]. So, "*3A4" would mean made at Amperex Hicksville factory, in the 4th week of January 1963 -- a nice vintage!

The codes on the first line stand for [tube type] and [??]. "VR" means a 6DJ8 type (i.e., a 6DJ8, ECC88, 6922, E88CC, 7308, or E188CC). The significance of the last number is murkier - it seems so signify the number of the batch or production run. Whatever it means, the lower the number, the older the tube. So VR4 is older than VR6.

Tubes made at the Hicksville factory were just about always branded Amperex and tubes from Blackburn were almost always branded Mullard. But the Heerlen factory pumped out a lot of (excellent) tubes and they could have been branded Philips, Amperex, Mullard, or Valvo. The Valvos usually sell for a little less; I'm not sure why, but the Valvo name is less prestigious and some assume that a Valvo was made at Valvo's German factory (not as good, imho). But if the factory code indicates Heerlen, well, a Heerlen tube is a Heerlen tube. The brand name means nothing. They're excellent.

The good news is that, even if your tubes were made at the same factory, they're all good, just different flavors, and you would have two nice sets of tubes. 'Can't have too many toobs. (But take that with a grain of salt -- your writer has a drawer full of these -- which is what led me to research and get to know the coding.) Happy decoding, James
There's not a tube on the planet that needs 200 hours to break-in.

Perhaps the listener is acclimating to the new sonics as he hears familar software with different tubes.
Bill is right. Tubes require less break-in than just about any other electronic device because they have *literally* a vacuum as their primary dielectric.

The concept of "break-in" is really a convenient name for the process of forming the dielectric or insulation layer around a conductor or conductive element.

Part of what makes tubes sound so great and break in so quickly is that there is no insulator surrounding the conductive elements- not even air!