MC901 monoblock tube matching Q

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."

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

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.

Nice the dream team 901's and C1100

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.