MC901 monoblock tube matching Q

It makes no sense to change tubes on a brand new amp. I don't think Mac would put inferior tubes in their statement monoblocks. I have a C1100 with the stock tubes & the sound is fantastic. Mac tech support told me that preamp tubes are good for 5 to ten years. 

Get yourself a couple of spares,and call it a day. Sit back,and enjoy the music. 

Looks like @crustycoot is correct. I called McIntosh again, this time got Chuck in technical support. He said neither the power tubes or signal tubes need to be matched in their amps or preamps. He did say it’s possible there may be a slight audible benefit if using matched sets, however. Guess that answers my questions. 

My understanding is all Mac tube amps use a biasing system that obviates the need for matching either power tubes or pre-drivers.  But sourcing your tubes from them should be the safe bet. If their parts guy doesn’t inspire confidence, ask one of the more senior tech advisors like Chuck Hinton. 

Nice the dream team 901's and C1100

Thanks for the replies, all. In addition to the MC901’s I’m also running a C1100 (tube preamp). One of my tubes is microphonic, which got me thinking it might be a good idea to keep a spare set around (especially considering the Russia situation).

From some quick research, I get the sense that power tubes (KT88) should be matched, but that signal tubes (12AX7 & 12AT7) don’t necessarily need to be matched. Does this sound right to y’all? Although the language in MC901 manual makes it sound like nothing needs to be matched in those amps, at least from my reading of it. So, I’m a bit confused.

 

I contacted McIntosh and was transferred to their Parts Department, who informed me that "he’s pretty sure" the power tubes (KT88) should be matched and the signal tubes (12AX7 & 12AT7) do not need to be matched. Not confidence inspiring.

For simplicity, it's easier to just order replacement tubes from McIntosh, as needed.

I certainly wouldn't go replacing tubes until they have exceeded their normal life or, alternatively, fail prematurely.

From the owner's manual:

The MC901 will function optimally with any correct
tube type that is functioning within the design
specifications of the MC901. Only when a Tube falls
outside of the acceptable range will any diminishing
of performance be heard. Because McIntosh Tube
Amplifiers are engineered to use Tubes in a way that
does not rely on the Tube’s individual character and
can perform perfectly provided the specifications are
met, there is no advantage to seeking out expensive
esoteric tubes.
Over time, a Tube may fall out of the proper
specification range. New Tubes that meet the
MC901’s specifications can be ordered using the Part
Numbers on page 12. For the positions of the tubes,
see Figure 15. This pattern is found on each side of
the MC901

My advice to you is to leave it alone.  You didn't spend a bazillion dollars on those jewels to f around with them.  Many years from now when you do need to service them, ask a pro - not a board full of "experts."

The power tubes are in quads and the signal tubes are in pairs. You can just throw one in, it will work. How it will sound is a different story. I'd guess just fine.. How picky are you. 10 years from now, start looking..

Preferably yes, it’s always good to install a matching tubes.

Agree^. Bad timing. 

Now ain't the best time to purchase tubes. 

Holy smokes! Those should be able to crack the foundation!

Are you willing to describe the rest of your system to us who have naught to listen to but an AM transistor radio? What speakers? Preamp?

I’m very jealous!

Why are you looking for tubes on your new 35K monoblocks?  They certainly are not worn out yet, in fact they should last at least 10 years as the power tubes are not run hard at all. Same for the signal tubes.

This is totally obvious, but at $35K MSRP for the monoblocks be totally sure to get expert advice before retubing these beasts.  It's interesting, I did not realize that there were any combination solid state/tube amplifiers built.

Wow, that is quite an amp. Most tube retailers provide matched sets of tubes for no additional cost or a small fee. So why not get matched sets? Not sure what that amp really needs the manual says have your dealer replace the tubes, no help there but the power tubes are run by sophisticated electronics so it's probably one of those that doesn't require matched tubes but that is just a guess.  

Answer A:  Call the manufacturer and ask. 

Answer B:  If you can find a schematic, look at the tubes in a series stack or parallel stack and match those.   In general, you want the gain tubes to be as low noise as possible, so spend a few extra dollars and get super low noise tubes.   You won't need to match between amps, just match tubes within one amp.