Tube rolling 12AX7As

I agree with Newbee, if your preamp is new, let the unit and the stock tubes go thru a burn-in period. Otherwise you'll never know the true sound of the preamp and how it integrates into your system.
If you're curious, open it up to see what brand tubes McIntosh has used in your unit. But let the burn-in happen first before tube rolling and during that period you can research the different brands of NOS tubes and their sonic signature.

Thanks everyone for the wonderful replies. I will be heeding the advice. A few things......

The C2300 is not brand new. I have bought it used, with the original owner lightly using it. It has about 10 hours of actual operating time. I am assuming that 10 hours is not enough time for burn-in of the tubes. That leaves me to question, what is a reasonable length of time? 30, 40, 60 hours??

Secondly, for the first few months I will using the C2300 only via the headphone jack. The reason being is now I have to save up for an amp. I slowly but surely want to have a complete McIntosh system, so I am aiming for a completely refurbished MC240 (recapped with updated power supply) or a modern MC275. So I hope this does not seem like a stupid question, but will further burn-in occur while only utilizing the headphone portion of the preamp??

Lastly, about 80% of my music listening is via vinyl. That is why I chose the MC2300, for its phono stage. So if/when I wish to tube upgrade, the MM phono tube will be my main concern.

Either way, I will wait a few months before doing any tube rolling. Once more TYVM everyone for the advice thus far and recommended web sites!

Brad,

a good plan you have there and I admire your patience. Make sure and place the type of tubes in the preamp section that you want to use to flavor your system and you may wish to consider neutral tubes for your phono stage.

Now, I may be setting myself up for a flame or two but there will be some who believe breakin wont completely occur unless your preamp is connected to an amp. They are wrong and likely still live in their parents basement. As a matter of fact, they probably just dropped their video game controller while reading this heresy! LOL.

Brad, I would not worry too much about performing any tube upgrades until you get your amplification sorted and acquired. If I'm not mistaken, the headphone amp of the C2300 is an op amp so the funds spent on NOS 12AX7's might be better utilized presently toward your fund to purchase an amp. In other words, the addition of either amp would be top priority over flavoring the output of your preamp, which you likely would not be able to discern through the headphone outs of a C2300. My 2 cents would be to save for a 275, the 240 being kind of an enigma....not as sweet and lovely presentation wise as MC30's and not as crisp and articulate as the 275 editions. Good luck with your journey.

Newbee and Lowrider are correct. The C2300 is a wonderful unit out of the box and you'll want to know how it matches with everything else in your system before fooling around with changing its sound. Took me about 6 months with mine until I had a good handle on it all.

The 12AX7 and 12AX7A is essentially the same tube. In the 12AX7, there are variants used for their quietness, ruggedness and even broadcast and military versions. They even have balanced versions and general upgraded variants.

You'll want to familiarize yourself a bit before shelling out serious money for a NOS Valvo or Telefunken tube. The label often doesn't indicate the tube's origins when dealing with the NOS stuff. I've seen Valvo tubes that were actually Mullards and Amperex tubes that were out of Blackburn as well. There is a way to tell, but don't trust anyone but the most respected sellers until you figure it out if you get the itch to try expensive NOS stuff. North American tubes have similar problems, but they don't usually bring such a premium as the Tele's and Valvos.

As for the burn-in time, I've found that tubes need very little to reach their optimum sound...like less than 20 hours. They will also sound better after being heated for 30 minutes or so.

For what it's worth, if you don't need all the gain of the 12AX7, the lower gain 5751 can really impress and all that I have ever seen are very rugged with closely balanced sections. You wouldn't want to use it in the phono section, but the preamp might like it. There is just way too much gear that uses far too much gain in their designs. Whether or not your Mac falls in that catagory, I don't know.

Congrats on the Mac, btw.