MC275 Tube Rolling...

Sorry on the above post. Meant to write Gold Lion.

I've never owned a Mac amp. I'm presently using a Music Reference RM-200 but I just want to inform some of you , who may not aware, of a very little talked about KT-88 tube. It's called Canada Fuller. I've read it's designed in Canada and manufactured at the Shuguang plant and I wish I could find more information on it besides that. My favorite KT-88 before that was the Golden Lion. But this tube, to my ears, has better bass, and more detail in the mid range as well as in the highs. I first bought it from Parts Connextion, but now I can only find it on eBay. It's a sexy looking tube and so far, after over a year of using it nearly everyday, it seems to be reliable. Just a heads up, for some reason the prices have risen nearly $80.00 since I first purchased it. But I intend to buy another set as a back up. Just my 2 cents and a recommendation.

Tell us, please, what you hear with the new tubes?

Thanks (RWD)

5 years later, I have settled down to the following tubes...

KT88 Gold Lion
(will try black treasure one day)

V1 (12AX7A)
RCA GP 12AX7A

V2,5(12AX7A)
Mullard Blkburn GP 12AX7A

V3,4,6,7 (12AT7)
Sylvania Gold Brand TMBP 12AT7wA (aka 6201)

Lots of talk about this tube so I bought a quad set; hopefully, what I've read will be duplicated in my system...

Thanks for such an interesting comment! I've a MC275 MKV and I would like to retube it. Now, my main concern regards bias, as I've been told that electric parameters between valves can change significantly. In a nutshell, I would love to replace factory tubes with Genalex 12AX7 and 12AT7 and Genalex KT88 or Shuguang Treasure KT88 or Tungsol 6550 instead of factory KT88, but I'm quite scared of potential bias consequences if it can cause any harm to my beloved Mc.
Could you kindly give me some suggestion or assurance before deciding what to do as you seems much more expert than me....
Many thanks

The folks at Grant Fidelity have asked me to update the link to the Shuguang Treasure series KT88 which appears in my previous post. The new link for these tubes is http://grantfidelity.com/site/Shuguang_Treasure_KT88-Z

The "A" designation simply refers to a filament configuration that allows the tube filaments (there are two "tubes" in a single bottle) to be connected in series or in parallel (to accomodate 6.3V or 12.6V power supplies.) In the 275, you can use any 12AX7 or 5751.

As for tubes, I have arrived at certain preferences (none of the ones previously mentioned here;-) but there are lots of opinions and it gets a bit like discussing cables (though not quite so bad!!) I will agree the stock tubes uniformly suck! Now that wouldn't be such an issue, and ordinarily I'd just mention it in passing and let people discover alternatives on their own (or not) except that besides sounding crappy, they can be dangerous -- to the amp! I can't tell you how many new (and usually new to audio ;-) MC275 owners have had KT-88's arc/short and blow fuses (and minds!) And if the fuse doesn't blow fast enough, or you don't hit the power switch fast enough, it can fry a plate resistor or worse and then it's going to be more complicated than just replacing the faulty tube(s). So I recommend changing out the power tubes immediately - for insurance reasons, not so much for listening pleasure - that's just icing on the cake ;-) Either the Shuguang/Penta KT-88SC or reissue Gold Lions are very reliable and sonically more robust than the OEM Electro Harmonix (although the "sound" of an MC275 comes first from the choice of 12AX7's, then the 12AT7's, and last the KT-88's. There is also a new (haven't heard it) Shuguang 50th Anniversary black glass KT-88, very sexy looking ;-) http://grantfidelity.com/site/Shuguang+Treasure+KT88-Z and $258/pair. Heck, if you're a shopper, you can find a pretty good used pair of original GEC Gold Lions for that kind of money and really be in business! But as I said, I haven't heard them, and the KT-88SC's I tried were quite impressive.

As for tube matching. McIntosh is semi-correct in saying it's not critical to have closely matched power tubes in their amps. That's because the Unity Coupled Circuit design doesn't rely on critical tube bias adjustment. The Mac PT bias is actually set to a fixed value at the factory and that's it! One reason they (McIntosh) can get away (most of the time) with sloppy matching of the KT-88's is because the OEM EH KT-88's have a rather low power curve (5000 Gm max.) whereas Shuguangs and new/reissue GL's are 7000, and NOS GEC's or Gold Lions are 9000 - used!! And even at 5000Gm, the the stock tubes often fry, and I'm convinced (though I can't prove it) that it's because they're not better matched. So if you're getting new PT's, get a matched quad and be done with it (better yet, get 5 matched tubes and in the unlikely event one goes bad, you can drop the spare in anywhere without worry or having to buy a new matched pair for that channel ;-) Otherwise, you can rotate the 5 tubes every 6 months like tires -- I'm serious! ;-))

The 3 latest MC275 models (the GG/Gordon Gow Commemorative, the Mk-IV and the Mk-V) have balanced circuits (I finally realized that's why they're the only three models with XLR inputs -- duh!) If you are driving the amp single ended, the V-1 tube IS in the signal path in order to convert the incoming un-balanced signal to a balanced signal to drive the rest of the amp. Each side of this double-triode tube handles one channel. So it's CRITICAL that both sides of this tube (regardless what brand) have matching Gm (which stands for transconductance or gain) otherwise your channels could be unbalanced; and since they dropped the gain controls on the model V (Infinity-Audio,) you can't be fixing an out-of-balance tube at the amp anymore. V-2 and V-5 should be reasonably matched (within 20%) both internally and with each other. Ditto the pairs V-3,4 and V-6,7.

If you eventually acquire a preamp with balanced outputs and can drive the amp balanced (highly recommended) you will still need to keep some 'ole 12AX7 in the V-1 position to complete the filament circuit, but it won't be doing anything with the signal, so it need not be something expensive -- even one of the OEM 12AX7's will do ;-)
.

Do we really need to follow Mac's instruction for using 12AX7A? or the regular 12AX& and 5751 will work. I am talking about the v1, v2 and v5 position.

If I am using unbalanced input, is v1 in use? Will changing the v1 tube affect the sound more or the v2 and v5 changes the sound more?

Mullards, Telefunken and Amperex are the most common used for 12ax7 and 12ax7a in preamps and amps. Some tubes have higher gain or low microphonics with warmer or darker sound.

Magnumpi205 described it pretty well.

Genelexs are in three of my amps. Great tubes. Reasonable price.
Amperex ecc83 are the best of the bunch for sound and longevity. Also,can use-12ax7,12ax7a,7025,7025a,6681,ecc803,ecc803s, plus others.
Telefunken ecc81, slightly dark but very clear and clean. Also can use-12at7,12at7wa,12at7wb,ecc801s etc.
These tubes range from common use tubes to commercial to military grade.
You can pretty much tune amp to your ear.

I also realized that on the chassis it is printed 12ax7a. What is the difference between the 12AX7 and the 12AX7A? Will it be okay if I use a 12AX7 instead of a 12AX7A?

Made a decision that I am going to give the Genalex a try. Still want to know whats good to roll for the 12 type tubes...

Hi Jgiacalo,
I am a happy new owner of MC275, in fact, I like it so much that I am getting a second pair so I can run them in mono. I wonder in your experience, does using the Herbie tube damper "sucks" the life out of the music?

Right now, I like what the MC275 does in my system from mid to high, the sound is very sweet and lifely. The bass is not bad, but below 40Hz it starts to get a little 'loose'. My speakers are only 85db efficient, but one single MC275 can drive it to 110 db loudness easily. I can't wait for the second unit to arrive.

Thanks for sharing.

I have re-tubed almost all of the smaller tubes (12ax7's and 12at7's) with telefunkens. I was a bit skeptical about how much sound improvement I would get but I certainly did hear a better difference. While waiting for a second set of tubes for my 2nd Mac 275 (I have 2 running in mono) I could distinctly hear the difference between the right and left channels (Telefunkens vs stock tubes).
I have yet to replace my KT88's but plan to do so.

RWD
Rick

Lapierre makes an excellent point about matching tubes. Sound advice to follow.
I'm using a McIntosh C2200 as my pre and it is a great match for the 275 so I think your interest in the c220 is well justified.
I started on the tube-rolling path when I noticed my stock KT88s were pulsating blue light. It was weird because you couldn't see it looking directly at the tubes only out of your peripheral vision. I thought it was just my aging night vision until my wife noticed it, too. The stock tubes don't last more than a year, if that. But even if they're still good you will be rewarded with rolling to better tubes.

I have a Silverline Sonata MK I. I am planning to go with a Mac C-220. I have to tune it as the sound is now not what I want, and I am trying hard to find out what tubes, which brand, what production will have what affect in what area... I am excited to know what you guys have settled down with and why... More input is definitely appreciated!

Another insight is to match your 12types during purchase. Whether you select Mullards or Telefunkens just make sure the vendor tests all the tubes as matched pairs. Same goes for KT88 you want a matched Quad of KT88/6550 regardless if it's NOS Genalex or GE, JJ/Telsa Blue Glass, Electro Harmonix, EAT, or SED.

FYI. Last year I knew nothing about tube rolling. Nothing!! But I was forced in to action because I started to hear popping sounds from the stock tubes and then my fuse blew days later.

Several phone calls later and hours reading on the web (GON and tube sites) I had answers to my questions.

What is your preamp and loudspeakers?

For the KT88s the best I've found, and reasonably priced are the current production Genalex Golden Lion KT88. They are vastly superior to Russian Lyting "C"s, Electro Harmonix and the stock McIntosh tubes. There are several online sources for the Genelax tubes. Then, add Herbies tube dampers (to all tubes) to reduce microphonics and you've got a really dynamic, rich tube set. For the 12AT7s and 12AX7s you can't go wrong with either Mullards, Telefunkens or Amperex Bugle Boys. The Shuguang triple mica have also been recommended to me for the small signal tubes but I've not heard them.
I realize that McIntosh uses the stock tube sources to insure production supply continuity, but the tubes I mentioned above will transform the MC275 and bring it to an entirely different (superior) level of performance.
The 275 can also be further improved by setting it on three Mapleshade Heavyfoot V3 brass footers.

'audio classics' may have some thoughts on this.