Tube rolling, Macintosh MC275 Mk IV

Thanks! Very useful info.

Not too surprised about the Penta Labs solid plates, they're pretty nice in a couple of other amps in which I've tried them. Nicer than any other current production KT-88 or 6550 I've tried. Not quite as nice in my Citation II as the original Tung-Sol's but better in the 2 AR amps I tried.

Fun stuff!

gentlemen:

i have had repeated discussions with chuck hinton about the design of the circuits in the 275 amp and c 200 preamps.

his comment is that the design of the tube circuit makes both amp and pre amp tube insensitive. i have had the c 200 preamp for several weeks and tried 4 pairs of 12ax7, namely, rca 12ax7 grey plate, rca 575a black plate, mullard 12ax7, tungsol 12ax7 and sylvania 12ax7. differences were very slight.

i have not yet experimented with my 275 mark v.

there are 2 types of errors in listening. one may hear something which is not there or fail to hear something that is there. i am very puzzled, as i am very sensitive to the upper mid and lower treble frequencies.

Tennis, I haven't any experience rolling Mac preamp tubes (for one thing I don't have a tube preamp.) Generally speaking, an amplifier (of whatever stripe) has more affect (along with the speakers of course) over a system's sonics than anything else, simply because that's where the signal is magnified many times. In any case, hearing is believing, and the differences we experienced were not subtle -- especially between the stock Mac tubes and all the others. And, as I indicated, I purposely included non-audio folk in my tests to avoid any audiophile "wishful hearing" ;--)

Mr. Hinton must be politic in his remarks, of course. But if you go over to Audiokarma, you'll discover that Ron Cornelius (McIntosh Product Manager) is using Penta Labs KT88SC's in his new 275; and although he won't/can't say, has probably changed out all the little McChina tubes as well. I got the same line from McIntosh as you did, but try and keep your thinking open, and you could reap unimagined rewards.
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Mrtennis - I am puzzled. The C200 preamp is all solid state. Are you referring to the C220?

my mistake. i am referring to the c220.

regarding the 275. chuck hinton told me a funny story. he said a customer placed 12at7 tubes in the sockets marked "12ax7" and placed 12ax7 in the sockets marked "12at7".
the result ? no damage to the amp or tubes.

i have several sets of 12at7 and several sets of 12ax7. i will keep an open mind and see if i hear any meaningful differences.

my experiences so far with current production tubes components is that replacing stock tubes does not significantly alter the sound. that is, what differences do occur don't matter.

my experience includes cd players and preamps.

i would love to be present at some of the sessions cited by audiogon members where several sets of nos tubes replaced stock tubes. it is possible that my threshold for experiencing meaningful differences is greater than that of other audiophiles.

i will report back after i have investigated the effect of replacing the stock 12at7 and 12ax7 following the break-in of the mc 275.

Tennis, when I get them back from the individual quoted in my initial post, I'd be happy to send you some to try. (Maybe I should start a tube 'Lending Library, like the Cable Co. ;--) But if you go to Ebay and get three NOS RCA 12AX7 blackplates (or I know a seller who has them for around $25 ea. and they're money-back guaranteed) you can hear for yourself. If you're smart enough to choose an MC275, I'm sure the rest of your system is good enough for you to hear the difference ;--)
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I know this is a '275 thread but I wanted to share some of my anecdotal experience regarding tube rolling in Mac gear.

But first...
I was at the dealer and we unpacked the large MA2275 first to make sure everything worked. Then the dealer and I started inserting the 12ax7/t7 tubes into the sockets. We didn't know at the time that we placed the 12aT7 into the 12aX7 sockets and vice-versa for the other 12aT7 sockets... we didn't know at first and we listened for a few hours... we (including the other salespersons) were marveling at the sound and then a customer came in, looked at the amp and said, "hey you got the toobs wrong!" D'oh! After all that, there was no apparent damage to the circuit or the tubes as far as we could tell.. the resident technician yelled at us and then also marvelled at the lack of damage (and the good sound).
So we re-read the labels this time ;-) and re-inserted the tubes the correct way. More listening ensued and lots of customers drooled over the sound of this integrated amp. This was the first 2275 the dealer had ever ordered so it was a special treat for us to actually unpack and audition it at the store ;-)

... So the folks at Mac gave me the same story: "Tube rolling is futile..." Of course I was more tempted then ever to try rolling some KT88s. So out came the Mac toobs and in went some beautiful JJ KT88s kidnapped from my Cary Rocket 88.

Normally I'm open minded when it comes to these matters, and I was prepared to believe either side. Would Mac be right or would audiophiles save the day? To be honest I didn't really want to hear ANY differences because (selfishly) I didn't want to take my Rocket 88's tubes out of service in my other system. Also, I was very satisfied with the sound from the 2275 so why bother...

Well! I'd be darned if I didn't hear a significant difference from the JJ tubes. The most significant difference was a more extended, impactful bass. The soundstaging was a bit deeper and the highs slightly more extended. Wow! I was expecting at the most some small differences in tonality, but not of this magnitude.

I haven't even begun to roll some 12axxx tubes yet, and I'm sure there will be some sonic differences as well. The bottom line is that there ARE discernible sonic differences between tubes when rolled in Mac gear, just like any other piece of gear.

best,
-Greg

mullard cv4004's and cv4024's go very well with my Mac2102's. Takes away a little of the sizzle from the stk Chinese tubes and maintains great transparency

Downunder, I'm currently A-B'ing some Mullards and Telefunkens in the 12AT7 positions (see original post) and I'll report back. They seem very nice and open -- it might be a toss-up. We'll see (I mean, hear!)

gentlemen:

there is a question regarding the compatibility of other 12 volt tubes with the 275 circuit. i believe that a 12ay7 could substitute for a 12ax7. what about a 12au7, might that work in lieu of a 12at7 ?

is anyone willing to try a 12ay7 and/or 12au7 ??

i realize this is partially off topic, but i substituted a pair of 12ay7 for the 12ax7 in the c220 preamp. i also substituted a pair of 12au7 for the 12ax7 in the same preaamp. the preamp did not blow up and the tubes were not damaged. in fact i preferred the 12ay7 to the 12ax7.

By substituting the 12ay7 tube for the 12ax7 you are lowering the gain factor by approximately 50%. The 12au7 has a gain factor of approximately 80% less than the 12ax7 tube.

best regards

Another happy Mac owner (he has an MC2102):

Hi Neil, Just got back from Jamaica and my NOS from Marty were waiting for me. I just rolled in the Telefunkens 12ax7's and I want to tell you....wow. The improvement is unbeleivable in all parameters, especially with mid-quality recordings that were rather flat, (compressed?). They have opened up with much more detail and depth....quite a treat! I still have the RCA 12ax7's, Tele 12at7's, and 8 new Penta Labs kt88sc's to try out... expecting more great results. Thanks for steering me in the right direction, especially with Marty. Regards, John

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the gain differences i noticed in the preamp, were of minor consequence. what happens in the amp if i substitute 12ay7 anf/or 12at7 for the 12ax7, will the changes in gain be of more concern than those accruing from the same substitution in the preamp ?

thanks

Tennis, you can sometimes substitute differently numbered tubes in circuits without trouble (always check with the manufacturer first!) but then you'd be comparing apples to oranges sonically. Guitar players often substitute these lower gain tubes in their amps just so they can over-drive them and get the distortion effects they want. But I can't understand doing that in an audio amplifier; it seems counterproductive to me.

"Tube rolling" generally means trying different brands of the same number (and design) tube, for the purpose of improving/adjusting the sonics of the amp/preamp/tuner. Substituting tube "types" is not the same thing.
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changes in gain structure can sometimes affect the performance of a stereo system. i have been told that 12at7 and 12ax7 tubes were interchanged, by "accident" with no harm to the tubes or amplifier. it is possible that using 12ay7 might provide a preferred presentation than a 12ax7.

our hobby is based upon personal preference. "playing around" with 12 volt tubes may be a way of attaining a "sound" that is desired.

"our hobby is based upon personal preference. "playing around" with 12 volt tubes may be a way of attaining a "sound" that is desired."

I would think, in this case anyway, the "personal preference" part would come when selecting the amplifier in the first place. If one has to go so far afield as to substitute 12V filament tubes for 6V to achieve certain results, maybe one should consider a different amp? But, to each, his own . . . . ;--)

Recently, I've been using some 5751 tubes instead of the 12AX7's (see Joe's Tube Lore: http://www.nickdangerous.com/misc/mghead/joestubelore.htm )
I thought I'd give some 5751 tubes a spin. Joe basically dislikes ALL 12AX7's and considers the 5751's far superior. The 5751 is a military/premium version of the 12AX7. It (generally) has 3 mica spacers instead of two with copper reinforcing rods and closely matched triodes. It also has slightly lower gain than a standard 12AX7, but not enough to be noticeable IMO. I tried three of Joe's top choices: The RCA, GE, and his favorite, the Sylvania Gold Brand (note, the old, 1950-1960 3-mica Sylvania Green Label is the same tube, and cheaper) and found the RCA to have a slight edge in the MC275 over the Sylvania. The GE was a close third IMO. But these things are a function of the equipment you are putting them in. However, I do agree with Joe that the 5751's are better than the two 12AX7's I liked best (Telefunken and RCA black/long plate.) They're not as expensive (yet!) as the NOS 12AX7's, so you might want to give them a try.

OK, separate (but somewhat related) subject: Substituting 12V filament tubes for 6v filament tubes. For instance the 5965 for the 12AT7's. This is NOT the same as subbing 5751's for 12AX7's! The 5965 has a larger filament current draw and could ruin power supplies if they're not designed to provide higher filament current. Be careful, I think the MC275 PS could be damaged!