Mac 275 questions........

After some months of up's and down's with my ASL Hurricanes (just seemed to never stay operational for longer then 2-3 months) I have decided o retire them and get the McIntosh MC 275 (2 amps).

I have some questions for you all and appreciate any input you may have (especially form Mac owners) but opened to all.
My speakers are Infinity RS 1-B's and I will be using the amps to drive the top end of the system (EMIM's and EMIT's). I have a Perreaux 3150B for the bass columns. The Infinities are rated at 4 ohms.
I plan to listen to one amp on top ( I will get one amp in a week) and then when I get the 2nd amp ( a week later) run both in mono.
What will I hear with each application? First with one and then with both? Also can any of you let me know if any of you compared the Mac 275 (in mono) 150 watts with the Hurricanes 200 wpc? The Hurricanes were great but I just could not live with them being up and down so many times.

Thanks to all for your input.

RWD (Rick)
Had the origanal and now have the new. Built like a tank, plays music, not real tubey but not harsh like some solid state gear.
Can drive most anything. Should be a good match with the Infinitys, especially used in the mono configuration.
My other Mac pieces are over 40 years old and going strong. Worth as much now as when new.
Hi Rick! I love mine. The new ones are actually 90+ watts/ch (180+ in mono) so I think one amp should be sufficient for all the EMIT's and EMIM's. And though having two separate power transformers is nice, the one in the new model is 490V (the old was 420V I think.)

Speaker cable choice is very important with stats and planar electrodynamic drivers like yours. They should have very low capcitance (< 40pF per foot) and inductance, and they should actually have a little resistance.

The only cautionary note for the 275 is: Lose the OEM tubes immediately! (Save them for resale;-) The McRussian power tubes blow up regularly (and sound crappy) and the McChina signal tubes can go gassy and blow up a power tube (and they also sound crappy ;-)

If you need more info, let me know.

Hi Neil, Thanks for the response. Which tubes are you referring to...the KT88's? What do you recommed? I have someone who works in NY for a tube dealship so I might be able to get some new tubes at a savings. Your comments are valuable!
My (moderate priced) tube recommendation would be a quad of the new reissue Gold Lion KT88 (about $200) and some NOS Telefunkens for the 12AX7's and 12AT7's. If you'll send me your email address, I'll give you more details when I have some time.
Neil, thanks for the heads-up with regard to tubes on the 275. However, this is the first time that I have heard of failures (tubes blow up) from McIntosh? I totally agree that better tubes will probably improve (change?) the sound but I hope I am not going from the frying pan into the fire? That's the reason I am loosing the Hurricanes.....amp failures.

RWD (Rick)
I just got 2- 275's. Im waiting for the C-2300 to come in to hook them up. Where are the stock tubes made? I am curious about the tube failure? That is a bit disapointing. I am also interested in the new tube replacment.
Yes Chiroman, we will have to compare our finding when we get both amps up and running. My 1st map will be in this Saturday (Jan 5th). The second should be in a week or so latter. This will give me some time to evaluate the 1 versus 2 amps etc.
What are your amps driving?

RWD (Rick)
For now they will be driving Klipsch LaScalas, but I am getting a pair of Tyler Acoustic PD80s. My Preamp should be here tomm or wed. Sounds like you have some serious speakers? Got a website for em'? I would like to check them out.
If you go to and search the McIntosh forum on AudioKarma, you'll find lots of 275 info and owner experiences. McIntosh used to provide the finest tubes with their new equipment such as Telefunken and (English) Gold Lion/Genalex, etc. For one thing they were plentiful and not particularly expensive.

Today, companies that make tube equipment have to favor price and availability over quality -- so of course NOS is absolutely out on both counts. The KT88 power tubes Mac uses are Electro Harmonix made by the American-owned New Sensor Co. in Russia. They have bought the rights to many old brands like Mullard, TungSol, Genalex, Svetlana, and would like you to think they are re-issuing the genuine article(s) but they aren't (mainly because they don't know how to make them:-) BTW, you can still get real Svetlanas from the S.E.D. company in St. Petersburg, now sold under the Winged-C logo after their company name was sold out from under them!

The Mac signal tubes (12Axx twin triode-types) are Chinese, made for them probably by Shuguang. If you have a new Mac power amp with OEM tubes, my advice is to run it for 5 hours or so without any power tubes, so you can find out if the little signal tubes are going to hold up (I even do this with NOS/vintage tubes too) If a little tube dies, it dies (no problem, and certainly no problem in a preamp) but in a power amp, it could take out a power tube (again, not a problem if it's a cheapie power tube ;-) BUT, a shorted or runaway power tube can damage bias and plate resistors, and even power transformers, and that's where the repair hassles and expense begin -- and unfortunately, the fuse doesn't always pop fast enough (which is why I keep my finger on the trigger when I'm using tubes with reported reliability issues!

On the positive side, tube problems usually show up very soon (1 hour to 1 month) and once they're past that, you shouldn't have to worry (but I NEVER leave tube equipment on when I leave, not even a tuner!) Also, problems usually occur during turn-on/warm-up, so once things are stabilized they're OK - usually ;-)

The thing to remember is that tubes have been used reliably for the last 85 years, and often in critical locations (like ICBM's) so don't discount their quality. The problem is that tubes aren't tested and then burned-in the way they used to be -- certainly not by manufactures (they are by many online tube sellers such as Upscale Audio)

I'm using a quad of NOS Genalex KT88's ($800) and a quad of GEC/Genalex 12AT7's ($250) in my 275 and never a hiccup; plus they last twice as long as the reissued tubes.
Gene, just click on (system) by my name (RWD).

Hey Neil, I was going to purchase some tubes at New Sensor....perhaps we should talk off line? Their new Gold Lions 88 are not that good. Where did you get your tubes?
And thanks for all your support and help!

RWD (Rick)
Rick, are you going to put new tubes in, or are you going to run the stock ones for a while? No UPS today... Perhaps I'll get the preamp wed.?
I probably use the stock tubes initially. I plan to speak with Neil (Nsgarch)about some tube rolling.
Keep me posted on the pre-amp and amp!
Keep me posted on the tube roll... For now I have my Klipsch's hooked up to an Adcom GFR700 crankin some ELP Brain Salad Surgery... Great cd... It will do for now...

Keep me posted on your system. I have MC275's x 2 with C46.

I should have my system up sometime this coming weekend.
Lapierre --
The reissued GL KT88's are a good choice from what I hear, and cost about $200+ for a matched quad. The PentaLabs/Shuguang KT88SC's which I tried (and liked) are just as good according to many, and about half the price. Try Doug's tubes he's very nice, has reasonable prices, and he sells both.

For the AX's and the AT's, NOS Telefunkens are the minimum place to start. THE 12AX7's AFFECT SONICS THE MOST. There are three of them (V-1, V-2, and V-5) If you are using balanced interconnects (which you should be, with the C46) then the first 12AX7 (V-1) is not in the signal path and so it can be any ol' 12AX7, just to complete the filament circuit.

The first tubes I substituted (for the OEM tubes) were a pair of ratty old TFK 12AX7's (in the V-2 and V-5 spots) and the difference was really amazing in all respects -- air/ambience, detail, dynamics, soundstage/imaging, good hi and lo freq. response. Then came the TFK 12AT7's, and finally a quad of the Penta KT88SC's. The total should run about $300 - $500 depending whether you buy the TFK's on eBay or through an online tube seller. It's hard to beat NOS Telefunkens, but you can. Particularly by substituting Sylvania or RCA 5751's (triple mica black plates) for the 12AX7's. But the price/value ratio starts to go down as with all things audio ;-) (A pair of Sylvania 5751 TMBP goes for $150 or more these days -- but boy do they sing!)

You might want to read the 12AX7/5751 sections of Joe's Tube Lore, if you haven't:
Thanks Neil for the advice on tubes. Lapierre and all I also expect one amp this Saturday so I will keep all posted!!!
Just an update....the Mac's are in but I am only using one so far. I want to get a good understanding of whay one can do and then put them in mono. Hold tight!

Rick (RWD)
Nsgarch, I have read wonderful things about the EH KT-88. Have you ever tried them in the Mac 275 or 2275? Thanks.
Gavetti, it's the EH's that Mac now uses as their OEM power tube. They are both unreliable and crappy sounding -- one getter, low vacuum/thin bottle, yuk! I can honestly say I have experienced these attributes first hand! Back in the day, when the MC230,40,60,75 etc. established their great reputation(s) Mac was using genuine english Gold Lion and Gold Monarch KT88's from England and American Richardson KT88's. Along with original GE and Tung Sol 6550's. Of course they only cost Mac a few bucks a tube back then ;-) At least Audio Research uses the (fairly decent) SED (formerly Svetlana) Winged "C" tubes.

I have read folks saying nice things about the EH KT88's too, but I can't help wondering about their hearing!. At least the damn things didn't blow up on them!
Do the 12Ax7s and At7s need to be matched?
Really?!? I didn't realize they are using EH! When did they start using them? My amplifier is 3 years old, and I was under the impression they used different ones. That's good to know. I have a 2275, and was about to replace stock tubes with a set of EH KT-88 based on a set of rave reviews I have read. I guess the safest bet is to get the reissued GL. Most people seem to be happy with them. By the way, I completely agree with your assessment of the NOS TFK 12AX7's. I bought them for my 2275, and the sound improved considerably. It's much cleaner, detailed, and airy.
Bosrt, I pasted the following from my AK post:

I was curious why some folks didn't find tube changes had much effect with Mac amps and others like myself (and friends) were astounded at the improvement. I'm a natural detective, so I couldn't just 'let it go' After asking everybody lots of questions, I realized that most, if not all of the people who were 'underwhelmed' had changed their power tubes first (or only!)

I changed my 12AX7's first. Not because someone with prior experience had given me a hot tip. But because one night right after I got my amp, a (vintage gear) friend came by to hear the new toy, and brought some old Telefunken 12AX7's 'just for fun' and we were both blown away! Only later I read where Ron C. (I think) said that in order of sonic importance, it would be the AX's, AT's, and last the KT88's.

You will definitely hear subtle sonic differences in power tubes if you change the little ones first. But the biggest difference between power tubes will be in power (duh!) and the EH's (when they work) are the weakest. They have transconductance values around 4500-5000. The Pentas and (I'm assuming) the reissued Gold Lions as well, are much stronger 6000 +/_. The strongest, are the NOS Gold Lion, Gold Monarch, and GEC KT88's which, when new, are 10,000-12,000.

McIntosh also declares that it doesn't matter that much to have matching pairs of power tubes (or even the little signal/driver tubes.) Strictly speaking, that's true. And just to prove it, they make no provision for adjusting the bias if they don't match! However, if you're concerned with tube life (power tubes), or with precise channel matching (signal tubes) then you'd like to have tubes that match. No, they don't have to match within 5%, or even 10%. I'd say 20% or better is reasonable. Except if you're using the single ended inputs, I'd recommend that V-1 should have its two internal triodes matching within 10% or better.

I just checked the tubes that I changed in my McIntosh Ma-2275, and they were the AT's...changing them made a big difference. Now, I'd like to see if changing the four 12AX7A can make a difference too. Telefunken never made 12AX7A. They used to make 12AX7's instead. Do you know if I can use those to replace the 12AX7A's? If not, do you have any recommendation in terms of what 12AX7A's I might use? Thanks, Giovanni
I got into it last nite and had some success.

I preferred Mullards in the V2 12Ax7. Nice bass and some cleanish warmth in the mids. Highs nice. A Brimar was too bright. The other 12Ax7 got RCA 5751s. All these were more open and detailed than the original tubes. Also brighter.

For the AT7s, Brimars were good and RCAs good. The AT7s were substituted with what I could find on hand. Didn't work on rolling here much.

I also found as I replaced more small tubes the instrument solidity and location stabilized with a guitar intro that I know well. Cibelle/cibelle 2nd track.

12AX7A's are simply 12AX7's with a filament center tap that allows them to be run in series or parallel. Not an issue with the Mac amp.
If one is looking towards the rear of the 2275 from the front, Which pair of 12ax7a is used for the phono, the pair on the left or the right pair?
Greg, the fastest way to answer that question would be to call McIntosh. While you're at it, order a service manual/schematic -- that's what I did.

You can also find out by 'naming' the phono input something else (on the menu screen) if you do that, the phono tubes won't light up when you turn the amp on -- at least that's the way their preamps work ;-) (It's a way of saving tubes and reducing heat if you don't have a turntable.)
Hey Gregpen, I have a 2275 and the tube slots/function follows. The best swap is what you have already performed, the 12AT7's in slots V1R & V1L. These peform the function of "preout" tubes and are VERY IMPORTANT. Slots V4 & V5 are for phono and V6 & V7 are for tone controls (bass/treble). If you aren't using a TT, then any ole 12AX7 is fine. Additionally, I have switched my tone controls to off on the front display, so, I have plain ole 12AX7's in those slots (V6 & V7) as well.
Ontjesr - Thanks for that info. From what you say, if one does not use the phono section and wants to get the best sound, one should use the best NOS 12AT7's, and use some plain new production 12AX7's.
Any suggestions on NOS 12AT7's from your experience?
I wanted to respond to everyone since I was the original author of this thread. I have been listening to one Mac 275 for 3 weeks now. I am getting the other 275 installed this weekend. I hope to report to all of you the outcome.
There certainly is a difference between the Mac275 (one) and the ASL Hurricanes. Some pluses and some minus.
Hold tight and let me do some listening Saturday and Sunday (before the game) and I will report to you all.

Rick (RWD)
Rick -- how's the dual 275's running?? Ordered a pair, a C2300 and the MT10 along with all new speaker/interconnect cables. Arrive next week. Just curious after reading this thread. Thanks
Funny you should ask! I am planning to write an update and later a review. Doing that later today (while I listen). Some very satisfying aspects of the 275 and some not so satisfying (compared to the ASL Hurricanes). Overall.....quite happy!

Rick (RWD)
Well it's been at least 5 weeks with one McIntosh MC-275 amp in my system and now I have, for over a week, installed the second one and I now have two mono MC-275's. So let me share my experience.

I'll cut to the chase and say that one mono amp is very similar to two. One 275 (rated at 75wpc) is powerful. Two 275's @ 150 wpc is more powerful. What do I hear? In a word "relaxed". A little more control but a bit more relaxed overall.

My comments of the 275 therefore will be generally a comparison of one (1) 275 (2-sounds pretty much the same with the additions above) versus the ASL Hurricanes DT 200.

Here are the pluses of the Mac over the Canes:

First- I got my mid bass (and bass) back in spades. One of my complaints with that the Hurricane amp was that it had a higher sensitivity compared to my other electronics. I wrote in my review of the Hurricanes: "The sensitivity of the Hurricanes was much higher than my previous ARC amp and therefore, I needed to fool around with the controls on my Infinity crossover to boost the output of the bass columns. The higher sensitivity made amplification of moving coils much easier, but seemed to be bright ,a bit edgy and the upper bass/mid-bass was missing. However, I was struck, immediately, with a new unveiled sound that spread instruments wider across the stage with much more clarity than before."

I am not an engineer nor a tech so what I may be explaining to you may not, in fact, be the reality. However, with the Mac in my system it mated better with my Aesthetix Calypso and reintroduce better mid bass and bass. How this could happen and be, since my bass columns are driven by a separate amp, I am not sure. I'm just the reported.

Second- The Mac is very clear and solid. It is there in your face. There is no drift or sway and it makes you feel like the amp runs at more power then rated.

Third- It is silent. And this is a tube amp? Wow.......

Now here are the ASL's pluses:

First- Stage width with the Mac is good. With the ASL it is great. The ASL add 5-7 more (imaginary) feet per side to the orchestra

Second- The ASL Hurricanes seemed more delicate and cleaner. Less colored? Maybe?

So here I am sitting with my system, enjoying my music and the biggest plus of all (Mac vs ASL) is that I AM LISTENING.
The Mac's have been on without a hitch. Knock on wood. However, just the feel makes me certain that the Mac's are far better in construction (far) then the ASL.

Remember, however, ASL has come up with a better Hurricane and I have not heard it or seen it but I must believe it has to be more reliable then the original. I just could no longer live with break downs with hurricanes.

Finally, if anyone is thinking of a Mac I say "YES". It is quite a wonderful amp with some character and style and plenty of power. And it keeps on running.......

P.S. I have not yet listened to the Mac with better KT88's or x7's or t7's which I plan to as I expect this would provide an overall better sound.

Rick (RWD)
Rick, first I want to add some information about the new 275's you may not have encountered:
The two latest MC275's have 490V (vs. 420V) power transformers. They put out almost 90w/ch (180 mono) even with the stock power tubes. With the better current manufacture tubes (PentaLabs, 'new' Gold Lions) it's more like 95w/ch. And even higher with vintage tubes from the GEC family -- which even lightly used, have transconductance values upwards from 9500 mMHOs!

Second, the few (but real) attributes you noted using two amps, are largely due to having a separate (and huge) power supply for each channel. If you were driving full-range speakers, you'd notice improved bass control immediately.

And last, every hour that goes by using the stock tubes is an hour of audio bliss wasted. You can't know this now of course, but the sooner you put in some decent tubes, the less you'll be kicking yourself later ;-) Any any sonic evaluations you might make now, no matter how well intended, you'll have to completely scrap later on, so why delay the inevitable?
OK all you technicians and amp designers a question. I am here sitting and listening to "Mallets, Melody & Mayhem" a great percussion record (thanks to the great Sid Marks) and I am hearing stupendous bass from my woofer towers now that I have my new Mac 275's running. This is better then when I had the ASL Hurricanes. My question is the Hurricanes and the Mac's are only driving the top end of my Infinity's not the bass columns??? Is it really a sensitivity issue?

Any answers or suggestions as to why the beautiful bass is back in full swing?
Anyone? No one to answer? Sorry if my question is confussing. Perhaps I should try a new Thread. This is an interesting question. No?

"With new amps on the top end of my system (Infinity RS1-B's) I am getting more and better bass from my system then with my ASL Hurricans. However, my bass columns are being driven by a Perreaux 3150B amp that's still in the system. How can an amp on the top affect the sound of the lower range???"
Rick, I won't speak for the others, but I don't understand what you've got running what ;-) Are you running the 275 on the main panelsand the (what?) driving the woofer towers? And you want to know why that should result in (apparently) better bass performance than when you were driving the mailn panels with the ASL's?
Correct, Neil.

How can a change in amps (McIntosh 275 vs ASL Hurricanes) result in a dramatic improvement in the bass when they are not even driving the bass columns. It's a Perreaux 3150B that's assigned to that duty. Someone suggest the sensitivity of the top and bottom amps were not matched. But I just don't get it?
The short answer is: the ASL's are 200w/ch and the 275 is 100w/ch (and the Perreaux is 200w/ch.)

Since the preamp is driving the Perreaux with the same volts as it's driving either of the tube amps, naturally the bass will sound louder relative to the panels driven by the 275 than driven with the ASL's.
Just an update.

I have changed all my 12AX7's in the Mac 275 to "used" Telefunken 12AX7's and the change was really noticeable. OK Neil, you can say it..."told you so"! Hah!

Anyway, the sound is cleaner, yet more delicate (or is ti more air around the instruments?). I have on order some Telefunkens 12AT7's and then I will replace the KT88's with probably the Gold Lions.
Just an update!!

Rick (RWD)

Glad to see you have the 12A7's updated. When you order the KT88's make sure you get a matched Quad for each MC275.

I have a lot of changes (tubes, fuses, and CDP modification) added to my system this week. I will report on that later.
Rick, I'm glad you're happy with the TFK's, (and that's ALL I'm going to say about that!) And the rest of your plan I think represents the most bang for a *sane amount* of bucks. I just hope you can stop there; I couldn't. (But then, I only have one amplifier to feed ;-)