Biased as an owner could be, I'm very happy with these amps, and have lived with many others(check my system page: "Crisis Narrowly Averted". The Atmas have a clarity and ease of presentation that few amps do. The midrange purity is remarkable, highs are crystal clear w/o being bright. Complex orchestral and other pieces are easily untangled allowing 3D images surrounded by air if the rest of your rig is capable.
All this is IF & ONLY IF matched with an appropriate choice of speaker. OTLs and MA1s in particular need to be paired with speakers with an impedance of 8ohms or higher. If you have 4 ohm speakers, you'll need an autoformer such as Paul Speltz Zeros, which might be good, or might affect the sound(I haven't heard them myself).
From a reliability standpoint, they're built like tanks, mostly only ever needing tubes to be replaced. Ralph and his team are superior at support to make sure you get the most out of your gear. That point alone is worth focusing on. Ralph is a rare treasure, and worth reading about.
One caution, they run warm, and although not a problem for me, some worry about that. Cheers, Spencer
The most truthful-sounding amps I've heard, but not everyone prefers such a presentation. The better the recording, the more you will hear the amps' virtues - if you listen mainly to compressed pop/rock you can do as well for much less cache. A fully balanced (input through output with no ground reference to earth) is a must to get the best from Ralph's OTLs. That said, I'm a very satisfied MA-1 owner with a lifetime supply of tubes and will delight in great sound for many years to come.
What 200w Class A mono blocks do you have? I moved from CAT JL2 100 w Class A triode to Atma-sphere M-60 for use with my Merlin VSMs with no regrets at all. The OTLs are magical with the right speakers -- as sbank describes.
Well then, you are used to heat - a good thing. Interesting that you are considering Atma; seems like a very different kind of amp. Obviously you have some very excellent SS amps, what is it about the MA-1s that are making you consider the move?
I own a pair of MA-1s from 1990, obviously very early in their history. I would be interested in hearing from anyone who also owns or owned MA-1s of that vintage, and either (i) upgraded them to current or near-current specs, or (ii) replaced them with a newer version MA-1. What I am looking for is some sense of a comparison between the old and new, ie to what extent the sound is the same or similar, and to what extent improved.
I agree completely with Sbank's description of the Atma-Sphere amps. With reasonable care matching speakers, the MA-1 amps are magic.
Jimjoyce25, I own Atma-Sphere MA-2 amps that were very early production MkII amps (mid-90's production). I sent them to Ralph to be updated to MkIII status with the new regulated power supply, new power supply filter capacitors, re-wiring of the output tubes, and a few other changes to bring them to current specifications. The updates should be similar to the update that would apply to your MA-1s. The result of the upgrade was absolutely astonishing in all parameters. Overall resolution improved, tonal purity improved, distortion lowered, bass impact increased materially, and there was a greater sense of "ease" across the spectrum coupled with greater dynamics. My wife and I were extremely pleased with the update; a very very significant upgrade in sound for an amp that we were already extremely pleased with. If you can afford the updates, I recommend you go for it. .
The MA-1s are teh best amps I have heard in my system. I did listen to many amps for a time. The next closest amplifier I have heard was the Pass Labs Aleph3. In may ways they share a lot in common - very highly resolving, musical without artifical euphony. Compared to the Pass, the MA-1s have a more natural midrange. I did get a couple upgrades. There were some resistors that were added to the output tubes on all new production amps that weren't in mine. I also had them make the Caddock Resistor upgrade at the same time. The result was the removal of a bit of midrange harshness that i had been aware of before the upgrade in cpomparison to the Pass, which was gone after the upgrade. They work well with my Talon Hawks without autoformers, even though the Hawks are nominally 6ohm speakers. The S30 with autoformer and M60swithout autoformer didn't do well on these speakers at all. The M60s with autoformers were OK, but not great. Also don't overlook the physical beauty o fhte MA1s. They look stunning with their polished stainless chassis, and rows of big 6AS7G tubes. The tubes are especially nice with their finned anode plates. If only the filamnets could glow white instead of orange. Oh, well. Oh, and you cna change the color of the indicator lights on the front panel with different lenses you can buy from Fender guitar amp dealers (Musicianh's friend)
1. Can you adjust the bias yourself? Or is it pre-set at the factory and does not provide for manual adjustment? (Mine have a manual bias adjustment. The sound improves significantly as you push the bias toward the recommended setting, but tubes blow more frequently at that point.)
2. Is there a built-in bias-meter? Does the bias remain steady? I have a digital multi-meter to measure bias, and there is a fair amount of variation in the bias reading before it eventually settles down.
3. How frequently do tubes blow? Is there a simple way to tell which ones have blown? (My eyes are no longer good enough to see the very thin wires in the tubes that indicate whether they are good or not.)
4. Do you use upgraded power cables? Was there a material difference when you first installed them? In what respects?
5. How much of a warm-up does it take to bring the tubes to the prime listening point? I found that it took 24-48 hours to get to that point, so I eventually would leave the amps on for days at a time. Sound was improved, heat was not good, tube life was not good.
I think you should talk with Ralph directly; you will get straight answers and he will not jam his gear down your throat; you will also gain a perspective of his goals and objectives that he is trying to acheive thru his designs;I have had this experience directly;well worth the call.
Rleff offers good advice about calling Ralph. He's easy to talk with and will give you straight answers. But, just so there's some response in the thread to your questions...
1. The newest production amps (MkIII) have an automatic self-biasing circuit for the output tubes, so manual bias adjustment is no longer required.
2. A meter is still on the amp, but is now used just for DC offset adjustment, not bias adjustment since that is now automated. (With the manual bias adjustment which I retained on my MA2s, the bias remains dead steady once the tubes have settled in. I check it once a month or so since it's easy to do with the built in meter, but I rarely have to make any adjustment. With the automatic bias adjustment now in the current production amps, this is not an issue.)
3. Changes to the wiring of the output tubes have reduced stress on the tubes making it less likely that a tube will blow it's fuse. (For those not familiar, the AS7G has a built in fuse that simply breaks in lieu of any spectacular display or sound. Thus the need to visually examine the tube for that "small wire" to which Jimjoyce refers.) Ralph continues to recommend a 48 hour burn-in on stand-by of the output tubes for longest life.
It's been three years since I've replaced an output tube, and the majority of my output tubes have been running for more than seven years. One still has to inspect them visually to find a failed tube. I've started using a large magnifying glass to take a look.
4. I use an upgraded power cord, but still find the stock Belkin cords to work pretty well. With the Silent Source power cords I use, I hear more solidity in the bass and a bit cleaner sound through the midrange. But, it's fairly subtle and I could live with the stock cords.
5. With the MA-2 MkIII amps, warm-up is finished in about 45 minutes, about the time it takes for my cartridge to start sounding it's best. I always shut the amps down when I'm finished listening for the evening (and I place them in stand-by when I make an interim stop of 15 minutes or more).
I own a pair of MA-1 Mk.IIIs and an MP-1 Mk.III linestage+phono. I could tell you how much I enjoy this combo, but I'd just start gushing. Both are quite revealing of up and down stream componentry and both become even more magical with NOS 6SN7s. I've spent time with the M60s, MA-1s and MA-2s - there are differences across the members of the Atma-Sphere lineup, but within the same revision level, they share the same design, many of the same bits, and to my ears sound more similar than different. Reviews of the M-60 and MA-2 are a bit more prevalent and they should give you a pretty good word picture of the sound of the MA-1.
At present I'm using 4 Ohm Audio Physic speakers (Avantis) and the MA-1s drive them just fine. I've tried them with and without the Speltz Zero Autoformers, and while the Zeroes work as advertised they are not entirely without their own sonic signature. Different speakers yield different results, but in no way do I find the Zero mandatory on my 4 Ohm spkrs.
Jtimothya, I know what you mean about gushing. I was thinking about Atma-sphere amps for a long time as I knew that my Merlins were very OTL friendly, but I was not so quick to change from my CAT JL2 which is a mighty fine amp. Well I finally pulled the trigger and let's just say I understand why there is so much brand loyalty for the Atma-sphere gear. With the right speakers (perhaps fewer limitations with the MA-1 and 2), OTLs are very special indeed, and the M-60 seems to be perfectly suited in terms of power for the needs of my speakers. I think Tim Aucremannk's review in Soundstage is very well written and captures the Atma-sphere sound very well.
As far as SS, I've not heard better than the Pass XA-30.5, and I assume Nelson's higher powered versions are just as good, and necessary for less efficient speakers.
A nice problem to have indeed - I still regret having sold my XA-30.5. I might get one again, but that would be three amps.... I think in both cases, from these two manufacturer's you are talking about two of finest designers around and choosing is ultimatley personal taste, they both excel at what they do.
Please remember what I'm about to tell you in my post is just my opinion and nothing more. It doesn't mean it's true to anyone else besides me, but it is honest, sincere, and the way I hear it. I was waiting to post hoping that someone else would mention what I hear so I wouldn't be the first to have a negative comment about these extraordinary amps. From the many positive comments of all the people who have posted I don't think at this point that is going to happen. Another caveat to consider from my post is that I most definitely have a hearing impairment from 35 years or so of working as a musician. My comments are made with all due respect to my friends who have posted to this thread and to Ralph.
I myself came extremely close to a purchase of Atma-Sphere MA-2 amps to feed my Avalon Eidolon Diamonds. I was privileged and fortunate enough to hear these amps 5 different times at length, once on the standard Eidolon which were my previous speakers, and four separate times on the Diamonds. I was assured that the amps were totally broken-in so I feel it is reasonable to rule out that as a factor and also because the problem for me was exactly the same to various degrees each and every time I heard them. For me, what they did so very very well almost caused me to buy a pair of MA-2's. This is why I feel it is important to post opinion. It was only until the last two times of hearing the Atma that I decided I wouldn't be able to get past the problem I was having, and in the long run the problem would become fatiguing for me.
First the positive .... this is actually an understatement. In this specific way the Atma-Sphere MA-2 ( latest and greatest version ) rendered the most realistic sense of transparency I've ever heard from an amp .... period! The openness and air of the sound-stage the detail, simply magic. WOW!!! The only other OTL amp I heard before the Atma was the Tenor 75 watter. The Tenor had this same quality but not to the same degree. The sound-space wasn't quite as open and airy, however texture density I felt was a little more truthful. Textures were IMO more full bodied and harmonically complex with the Tenor OTL.
OK, here it goes ............. the flaw I felt I just wouldn't be able to get past was the longer and more times I listened to these amps I became increasingly aware of an unnatural band of frequencies in the treble. Certain notes in the upper registers on piano, vibes, and violins for instance had a bite, almost like an overshoot of attack, kind of like the amp was trying too hard to sound fast in the high end. I'm sorry to say that for me the more I listened the more I was made aware of the fact I would not be able to get past this character in the long haul. I heard a parallel to the Martin Logan CLS 2Z speakers I used to own. Some of you may know first hand or read this about the CLS, in certain ways they were undeniably more transparent than other speakers, so transparent in fact the images were a little ghost like needing a little more IMO texture density to sound real. But the big problem was, because of the taxing load it put on amps paired with it, the upper frequencies had a glare and bite to it that on certain notes would be like looking directly into sun.
Again, my post is just my take. It is not meant in anyway to be disrespectful to the other poster's opinions giving here and I can certainly hear and understand why many people would choose the Atma-Sphere amps, the strengths they posses are so compelling. This is a sizable investment and I felt my opinion may be of help. I wish you all the luck in finding the right amp for you
Hi Tom, good to see your post! One thing folks should be aware of about the A-S amps is that the choice of 6SN7 driver tubes will make a big difference in the sound. In the MA-2s you heard at my house on the standard Eidolon, Tom, we were listening to Sylvania 6SN7-GTA tubes manufactured in the '60s. These have a very clean, detailed and somewhat airy top end. Put in something like RCA grey glass and the top will get much softer and sweeter. Do you know what 6SN7 tubes were being used in the MA-2s you listened to on the Diamonds?
I'm afraid I don't know the brand of the 6sn7 tubes that were in the other 2 pairs of MA-2 amps that I heard. I imagine it was the stock 6sn7 that were supplied with the amps from the factory.
Rush, I heard far less of this treble abbreviation in your system then the other two systems I heard with the Atma/Diamond combo. This is before you had your amps brought up to to the latest version. If I'm correct, the latest upgrade included the new caps. I have a sneaking suspicion that the new caps are responsible for the sound I'm trying to describe. To me it's ironic that I think the caps are also what gives the sound this tremendous sense of openness. It would be interesting to hear from others if they feel the flaw I can't seem to get past is innate to the new caps.
Rush, I also remember you and Ann having issues when you first made the upgrade. Do you feel these issues have completely dissipated over time with break-in? Or is there still some remnants of those reservations remaining? Thanks so much for your candor. Maybe a learning experience can come from this discussion.
Rushton's comments on the driver tubes are right on. I found a combination of RCA GT Grey glass with Sylvania GTBs to be just right, the RCA are a bit more "romantic" sounding than the Sylvania and just right in combination for my ears. Same thing in the preamp, where tube rolling changes the sound a bit from neutral to warmer - in general RCA (warm) Sylvania more neutral. I'm not sure that tube rolling would address what Tom hears, but it might.
Tom, it did turn out simply to be break in for the new capacitors installed as part of the update. It took 400 hours for those capacitors to break in, and I was concerned about it. Then one day the amps just clicked over and the magic was back. Ralph was surprised at the amount of break in time, too. (BTW, the update to my amps did not include the new V-Cap coupling capacitors that Ralph has since made standard for the MA-2. All capacitors sound different and I haven't yet heard an A-S amp with the V-Caps. From what I've heard, the V-Caps are exceptionally nuetral and take 400+ hours to break in, sounding pretty brittle until they do break in, but outstanding thereafter.) .
Rush, I could be wrong but I strongly suspect that for me the unnatural treble characteristics and slight thinness in tonal textures that I hear can be attributed to the V-cap, no matter how long they break in. I'm learning time after time there is always a trade-off, a decision to made, from both the design stand point and for us as consumers even at this extreme level.
I think there may be a price to be paid for the gains that this cap has made to the performance of the Atma-Sphere amps. Again this is only my opinion, and being that the virtues of the Atma-Sphere amps are so plainly obvious I strongly encourage others interested to audition so they may deduce their own conclusions.
Thank you Rushton, Tom, Pbul57, Tvad, and others for your comments and insights. I really appreciate listening to others describe the same equipment I've heard. Imo, the Atma-Sphere circuit - whether in the amps or preamps - is highly revealing of virtually any change made to it. I finally grasp what RK means when he talks about 'listening to the circuit'.
Having heard the amps and preamps with and without V-Caps, I find increased tonal depth across the frequency range with the V-Caps. 'Tonal depth' being characterized as the sheer amount of harmonic and overtone information accompanying the fundamental. What I have not heard from the V-Caps is an increase in warmth, or put differently, an increase in pleasing second-order harmonic distortion that lends a sense of 'fullness' to notes. Lack of fullness is not lean tonality.
Because I presently use the amps and preamp as my review references, I've been round and round debating with myself how best to characterize their sound in contrast with other gears. Crudely put, 'thin', imo, means lacking information - one is not hearing all the harmonics and overtones available to be heard within ones audible range because they have gone missing - all else being equal, lost in the circuit. At this juncture I don't believe the Atma-Spheres are lean or thin in tonality.
Hopefully I'll solve this with a better vocabulary some day, but for now the way I parse things is to say the Atmas have plenty of tonal depth, but do not display the same tonal weight as some other components I've heard. And I cash *that* out not as sweet/dry or rich/lean, but as warm/cool, where warm suggests pleasing distortions and cool suggests a more analytical sound verging on displeasing distortions (more odd order). The Atmas are not 'cool', but they're not warm and I presumptively think that may be what some folks intend when they say they're thin or lacking tonal texture. In effect, texture is distortion. The Atmas do not convey less tonal information, they distort less, but its less of what turns out for us humans to be a pleasing distortion, and its absence is noticeable if that's how you like your music. I struggle with this, and don't mean to say any other person's characterization is incorrect; I just need a way to put consistently into words the similarities and differences i hear between the Atmas and other gear that will make sense.
Thanks for the contribution and insightful comments to this thread. Is it possible for you to characterise your experience with the Atma amps before, during (break-in) and after when the sound finally settled?
IMO I do hear the Atma amps as sounding a little less dense in texture than what I would consider ideal or neutral.
Tim, Tom, are both of your observations with Atma-sphere preamps? I do wonder about the issue of "pleasant" distortion, and no reason not to seek it if it sounds good, why not? - but is this the sort of thing you hear in live, unamplified music?
My observations are made only about the Atma-Sphere MA-2 amps as I have not heard any of their preamps.
The reason why I wouldn't want a component that adds pleasant distortions is .... in my experience I find they mask other timbrel/textural subtleties at the frequencies being distorted as well as the frequencies just below and above. Any added coloration will get in the way of hearing the actual musical intent of the recording in question.
Where I feel most audiophiles disagree is deciding which aspect of accurate reproduction is most important. Some will say "dynamic linearity above all else" I don't think you'll find this audiophile with a Quad 57. But few would argue about a Quad 57's tonal accuracy. Much of this will be determined by the type of music one listens to. A person who listens to small jazz ensembles will have different needs then someone who listens to big orchestral works.
For me, I'm striving for a balance of all sonic virtues with no area severely lacking. In the long term I find this seems to be the most musically satisfying and sensible approach. From my experience there is no product that's best at everything.
Agree on no best at everything. I tend to prefer neutral because euphonic coloration is alays there, though possibly always pleasant. With equipment on the neutral side of things, different recording sound quite different from each other acoustically. The tradeoff for me is that good recording sound better and poorer recordings sound worse. It is a tradeoff for sure, and one chooses between these two approaches.
Pubul57, I've had the great pleasure recently to spend some time listening to an MP-1 in a friend's system. I'm impressed: very neutral, very resolving and transparent, very quick and detailed. The virtues of the A-S amps in a preamp.
I've not been as similarly impressed with the MP-3 (heard elsewhere), but the MP-1 is a stellar unit that would fall among my top candidates if I were making a change. .
Rushton, are your feelings about the MP3 based on the phonostage and the linestage? I'm using the MP3 with the VCAP and Powersupply upgrade and it sounds very good to me. I've heard more universal praise for the MP1, but I'm wondering if that is based on phono performance. If the MP1 is that much better as a line stage I would consider it.
I was quite fascinated with what Trcnetmsncom had to say about his perception of a high end flaw in the MA-2s. Tom's likening this flaw to the high end rendering of the Martin Logan CLS 2Z made clear to me what he meant, because I auditioned those speakers a long time ago and I disliked them right from the beginning just because of that. I have the latest version of the Ma-2s, haven't rolled the 6SN7s so far and I just don't hear what Tom hears on my particular speakers, the big Sound Labs. Not that I doubt the sophistication of his hearing, nor his experience with live music. I share that with him, being a regular concert goer and intimately familiar with the sound of both violin and piano and just cannot find the flaw he mentions in my particular setup, which he obviously heard on several occasions on different rigs. This may well be a hearing impairment on my part, because I am advanced in age, however my wife, who plays the violin also cannot find anything wrong with the Sound Lab's/ MA-2 rendering of her instrument. We listened again extensively to Hilary Hahn's exceptional rendering of Bach's Sonatas and Partitas and could not find this particular shortcoming. We then tried piano on LP: Martha Argerich's rendering of Liszt's b-minor sonata, an early DG 2530193, again the highs were clear, crisp, without a trace of harshness or brightness. So this is puzzling. The big Sound Labs are not an easy load, but obviously pair very well with Ralph's bigger amps. Possibly we have just struck it lucky with this combination and would have been equally unhappy, trying the MA-2s with the Avalons. No lack of "denseness" either, with our stators to our taste and ears.
Thank you Tom. I found your contributions both important and thought as well as "hear" provoking. Obviously we strive for the same thing, the best balance of all "sonic virtues" as you put it so well, with "no area severely lacking". Obviously your benchmark is your experience of the live event as it is mine. We may have different tastes and rigs, but it feels good not be alone in this.
Pubul57, my listening to both the MP-1 and the MP-3 have been as full function preamps playing LPs. You may have it right that my differing reactions come from differences in the respective phono stages, but I suspect that's not all that's going on. I will say that the MP-1 was a vastly more satisfying listening experience for me, getting in the ballpark of what I expect as the result living with the Aesthetix Io Signature with dual power supplies and volume controls. The MP-1 sounds like a great preamp. .
Amp-loudspeaker matching is no less important with Atma amps as with any other amps. I tried to make M-60s work with Talon Firebird Diamonds even using autoformers, but ultimately determined the match unsatisfactory to my ears. My present line arrays are a match made in heaven for the MA-1s. "Horses for courses" is no less true at the track, as any fan of the great John Henry can attest.
Is it possible for you to characterise your experience with the Atma amps before, during (break-in) and after when the sound finally settled?
Thank you Tom.
I found the amps and preamp more similar than different across break-in. Out of the box there was plenty of resolution, but the sound was a little tight and closed-in. Relatively speaking, tonality had a wee bit of a greyish cast. During break-in, which I counted roughly at 120 hrs for the preamp, and a little more for the MA-1s, music gradually became relaxed and seemed to flow with a more natural pace. Tonal colors made something of a transformation towards the end of the break-in period - they really blossomed - all of which was rather startling. That final leap came over a few days for the preamp, and, say, over a weeks time for the MA-1.
The subsequent addition of the V-Caps to the MP-1 took things back a step before going forward two. Highs and the mid-bass got a tad edgy and a touch of the greyish tonality returned. Over roughly 6 weeks, things smoothed out and the tonal colors deepened. Sonic memory is difficult, but I'm confident that tonality eventually improved beyond where things had got to prior to the V-Cap upgrade.
Fwiw, I find both amps and preamp sound their best after being on for 1-2 hours - the hotter their tubes the better.
Thanks for the kind and respectful response. It's nice to be able to discuss the audible differences we discern in components, agree or disagree, still have fun and learn from each others experience. BTW ... Hilary Hahn smokes!!!
I haven't heard it myself yet, but from what I know the Sound Lab/Atma-Sphere combo is becoming classic. I'm sure your system must sound fantastic.
Detlof, a live recording of a piano with a close up perspective may give you the best chance of experiencing what I heard. Something like a small jazz ensemble, recorded in a intimate night club played back at a "live" playback level. In particular, listen to the attack of piano notes about 2 and a half octaves above middle C and up. What I heard (at least) was a unnatural sharpness, glare, zippity-zing if you will on the attack of those notes. The sustained note also sounded too thin and glassy to me. I started to hear this treble abbreviation on a variety of instruments and recordings I'm familiar with.
Another thing I try to listen for is the density of timbre/texture as a sustained note gets louder. Take for instance, a tenor sax player who plays one sustained note, he starts the note out at a medium volume and increases it to a loud volume. The note doesn't just get louder, the density of the texture also becomes more vibrant and more harmonically complex, it fills with ebullient energy. To me, some other amps convey this sensation with more conviction.
Tim, I want to thank you also for sharing your experience. Who knows? Maybe it was still a break-in issue with the V-cap after all. Much of what you described about the V-cap break-in mirrors my experience. I think too many variables are at play here to know for certain.
HH sure does. I am glad you agree. Thank you for your additional information. I'll go an researching. I suspect, my Wavac phono pre kindly glosses over the shortcomings you mentioned, without being euphonic though, as was the case with the old Jadis gear I once owned, because today I had the occasion to try out a Boulder 2008 phono pre amp and heard exactly what you did, fiddling wildly with the VTA of my cart with no avail. But then it may be the cable between cart and Boulder not yet broken in. We'll see, but you may very well have a point, because the Sound Labs should be no less revealing than the Avalons from what I have heard. We'll see, respective hear, after all this is a work in progress. Cheers, Detlof
A question for NOS tube users - Howoftendoyou change 6SN7s? I have a set coming this week. I'm just wondering if I'm starting a very expensive and unsustainable habit.
I use Sylvania GTBs with matched pairs in the two postions A-S recommend matching. The straight Sylvania lineup is a good match to my Aesthetix preamp. With a different preamp, some other mix might be better. The Sylvanias were a nice improvement in resolution, openness and timbre to the JAN Philips that I had once upon a time. Life expectancy on these is in multiple years of heavy service. .
In the preamp I use matched RCA GTs which are a bit more romantic than the Sylvanias. The GTs are generally not used in the amplifier because they can't handle as much voltage as the later GTA/Bs. RCA or Sylvanias are proably the most used NOS tubes by Atma-sphere owners as they are relatively available, affordable, and sound good.
I swap tubes around every few months - there are many great combinations. NOS tend to last much longer than contemporary brands - or so everyone says - I haven't had a 6SN7 go south on me yet, so no direct experience.
MA-1 Mk.III --- Driver: Sylvania GTA or RCA GTB Tubes 2&3: VT-231 Ken-Rads (these positions have biggest influence on sonics, imo), RCA Grey Glass Tubes 1&4: VT-231 Sylvania, RCA Grey Glass, or VT-231 Raytheon
I really like the VT231 Ken-Rads in the the amps. They're still out there but getting a bit (more) pricey.
Couple notes: i) My Mark IIIs are in the traditional narrow chassis, so position may be different w/ the newer style. Driver is understood as position #5 at the edge of the chassis facing the output tubes. ii) For NOS, the driver position requires a GTA or GTB - something that supports a higher 450VDC plate voltage; the other positions do just fine with other NOS (eg. GT or VT231).
The preamp is both challenging and fun because of the phono section, where it is harder to get good *quiet* tubes - but its definitely doable.
MP-1 --- forwardmost 6SN7: VT-231 Ken-Rad other 6SN7: Electro-Harmonix or stock Chinese phono (12AT7s): CV4024 Mullards, '60's Siemens 12AT7s, 6201 Sylvania Gold Brand
I put Herbies Tube Dampers on 3 of the 5 6SN7 per channel and 3 of 4 12AT7s per channel. The dampers work well.
The gear is incredibly revealing of tube changes (for that matter any change) and tube rolling becomes lotsa fun. Good section matching w/in a tube is v. important.
Just in case anyone is unfamiliar with it, there is also a version of the MA1s that come with 4 12SX7 tubes in lieu of the 6SN7s. This is the version I own. Rolling 12SX7s isn't an issue, as there are not many to choose from. Cheers,
Spencer, we've not used 12SX7s at any time, but at one time it was a popular field modification. The 12SX7 has similar specs to the 6SN7 and it is easy to set op the filaments for 12V, so it was a way to get access to an unused tube stock.
Ralph, is there any problem using US made (e.g., GE) NOS 6AS7s with MKIII amps? I thought I read somewhere that they could be a problem with fixed bias amps (I take it the MKIIIs are not).
Please let's not forget that the Chinese-manufactured 6SN7s are actually very nice tubes. I've paid a bit of a premium for Sophia tester "A matched" metal base military pieces from DIY HiFi Supply, but still only $18 apiece.
Matched pairs of Baldwin labeled 1965 vintage Raytheon GTB are being sold by Brent Jessee, a reliable vendor, for $45/pair.
I just took a gamble on four supposedly "matched" quads of Baldwin labeled Sylvanias of late 50s/early 60s vintage with the BIG chrome domes from Ebay at under $15/tube. The photos are quite sharp and show very clean tubes with spotless pins. We'll see how they test on my B&K Model 700...
One needn't pay upwards of $100/pair or even much, much more for quality 6SN7s. Just doesn't make sense.
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