I'm new to tubes... I have 2x MC901 monoblock amps. Each amp requires 8x KT88, 4x 12AT7, and 2x 12AX7A tubes. Do I need to match all these tubes? And do I need to match tubes for both amps together (i.e. 16x KT88 matched, 8x 12AT7 matched, and 4x 12AX7A matched)?
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.
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.
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.
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.
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..
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.
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.
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.
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.
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