Thoughts and Opinions of a tube audio/single driver junkie


The thoughts below are all the evolving opinion of one person (me). These are opinions, not facts, and in many cases I'm making generalizations, so take this advice for what it is. Your ears, your room, your system...are all yours. So in short, your mileage may vary.

Single Ended vs. Push Pull

In general, I’ve found that single ended amplifiers produce a more detailed, more realistic soundscape than push pull amplifiers do. They can make a good recording sound so very real and in the room, pulsating with life and vibrancy and lit from within. The human voice reproduced through a single ended amplifier can be spooky realistic, but it requires a specific quality of speaker to truly appreciate.

The two biggest disadvantages that many single ended amps have are bass and power; some of them do not make much deep bass and many circuits put out less than 2 watts per channel. However, there are a lot of factors at work here beyond the circuit, the tube, and its limitations: the type and quality of the transformers, the type and efficiency of the speakers, etc, all have a big role to play. So poor bass performance is not always the case, and low power does not have to equate to low output. Some single ended amplifiers produce very low and very well controlled bass that rival the best push pull designs, and with the right speakers, 2 watts can fill a room with sound loud enough to bother the neighbors.

Push pull amplifiers generally have one big advantage over single ended amps. Power. Most push pull designs produce more power than single ended amps do, and this can be a big factor for inefficient speakers. If you have 82 db/wm multi driver monsters, you’ll have a hard time finding a single ended amp that will drive them to acceptable room-filling and realistic sounding levels. In that case, push pull amps will almost always sound better. In addition, I've found that some hi efficiency speakers (Lowther, I’m looking at you) actually sound better with a bit of power, and 12 or so watts of PP 6V6 can be a great thing! Push pull will fit most situations better than single ended amps will simply because of speaker compatiility, but they usually give up a touch of the palpability and “air” that single ended does so well.

This is a good excuse to have both.

Speaker efficiency

So this brings us to speaker efficiency, and its importance in matching your amplifier. If you want to play with the tiny flea-watt single ended amplifiers (think the 45, 1626 or the 71a) you’ll need speakers with the highest efficiency possible. With amps of under 2 watts, its my feeling that you should be aiming for speakers in the 97 db/wm range or above. More is better. That's not to say a 45 wont work with a less efficient speaker, it certainly will. But it likely won’t have the grunt to make the most satisfying reproduction of the program material. It probably wont “breathe” in the way that showcases what the little tube can really do.

Once you get into the 3-5 watt range, things open up a bit. 92 db/wm is a good minimum recommendation for amps in this spectrum. Of course, more efficiency is almost always better. It’s like having more horsepower under the hood. Sometimes you need a bit extra to pass on a hill, and having that power at your disposal opens things up.

So why aren’t all speakers efficient?

It seems that back in the day they were. When tubes were the standard, and small amps were common, necessity dictated that speakers were built to be very efficient. Then, in the mid-1960’s, things changed. The transistor came along, and suddenly amplifier power was no longer an issue. Making a hundred watts per channel became possible and affordable, and huge and powerful transistor amps became the norm in the marketplace, quickly pushing the tube amplifiers out of mainstream production. This opened the way for less efficient speaker designs, and we began to see some really inefficient designs in the speaker world, with massive and complicated muti-drivers and huge crossovers that burned up more wattage themselves than many single ended amps could produce in total. But the audio marketing folks loved it (think megapixels in today’s digital camera world, each year upping the ante with questionable results but compelling marketing copy) and each year newer, “better” and even less efficient speakers came into the market powered by the newest “improved” transistor designs. The tube amplifier was an antique and nearly obsolete in just a decade or less.

If not for some hobbyists in Japan and on the West coast, hifi tube audio and single ended designs in particular might have disappeared forever. Now we find ourselves in a kind of renaissance of tube amplification, with new and innovative designs being developed in DIY basements and small scale production houses, picking up where engineers left off 50, 60 and 70 years ago. In 1985 it would have seemed very unlikely that new production 300B tubes would be common in 2017, much less the real antique outliers like the 45 or the PX25. But here we are (thank God!).

Side note: Its worth noting that tube amplification was never in danger from the music industry side of things. Tube guitar amps have been the mainstay of many, many musicians since the very beginning, and that is still true today. While the hifi world may have become finicky about tubes, the people who actually make the music never wavered.

Why full range drivers?

A good full range driver will make music sound real. The ideal (dream) full range driver would faithfully reproduce all of the critical frequencies by itself, so there would be no need for separate low frequency and high frequency drivers, and therefore no need for a crossover. Because the entire spectrum is being produced by one driver, the full range driver is a point source, and our very sensitive ears don't hear that critical midrange being broken up from multiple points and timings as a multi-driver speaker design does. This is tough to do with one driver in the real world, and of course there are compromises at both frequency extremes, but namely bass energy. Not many full range drivers can make really low bass, say sub 60hz. But the midrange can be so wonderful that the lowest bit of bass often matters less.

The crude graphic below illustrates just how low in the spectrum the vast majority of music and voice fall. As you can see, almost all of the really critical information is below 4khz, and that is well within the ability of even a modest full range driver to reproduce with startling accuracy. Having all of that midrange information coming from a point source is what makes full range drivers sound the way they do. I’ve certainly found it addictive.

A very interesting breakdown of the audio frequencies can be found at Audio Spectrum Explained.

How can one watt do anything?

"Many audiophiles use high power amplifiers to get powerful midrange and bass sound. But excellent speakers refuse brute power. The most important goal is not 'Power', but 'Energy' and 'Frame of Tone'." —Susumu Sakuma

The “first watt” philosophy dominates the small single ended world, and in my limited experience seems to be valid. I’ve found Steve Deckert’s explanations to be very useful, and I’m linking to those here and here. As he says, “If the first watt sucks, who wants another one?”

To sum it up, think of an amplifier that puts out 3 watts per channel. The first watt theory says that the bulk of the vibrancy, emotion and character of the music lives in the first watt coming out of that circuit. The next two watts flesh that out a bit more, but they are supporting characters to that first critical watt of power. In order to hear that watt, you’ll need the most efficient speakers possible, and preferably one without a complicated crossover. (Think of the crossover like a speed bump; you need to slow down to get past it. If there is no speed bump, you accelerate right past that point never breaking your power band.) Without being hindered by a complicated crossover, that first watt of power flies straight out of the amp and hits the voice coil of the speaker driver without anything impeding it. You experience everything your amp can deliver, and this is where you get into the quality. If you can preserve that first watt, and if it's a good clean beautiful watt, you’ll hear the details, the romance, the power of the program material in a way that makes the most of everything in the audio chain. This is where the very best circuit designs, the very best components and the very best program material can all come together and shine in a way that is really something magical. And its what single ended amps are all about.

The importance of the circuit

The circuit is a factor that many audiophiles tend to overlook. It’s not sexy like fancy chrome plating or massive potted transformers. The circuit is hidden underneath and out of sight, a mysterious spaghetti mix of wires, resistors and capacitors. I wont pretend to understand the ins and outs of circuits or their designs. But, I have come to realize that the circuit is really the most important factor in whether an amplifier “sounds” good or not. If the circuit is not great, it doesn't matter what fancy tube you stick in your amplifier.

Circuits can be massive and complicated, or so simple it defies logic. I’ve found that in most cases the simplest circuits produce the most pleasing reproduction of the human voice, and just sound more natural overall. The small Jeremy Fix single ended 6SN7 amplifier I once owned had such a simple circuit it was almost ridiculous, and yet that amplifier produced one of the best sound stages and voice reproduction of any amplifier I have owned so far. Again, the Decware SV83 has only a few very simple elements in the signal path, but it is my number one newbie recommendation for any tube amp I’ve experienced.

One of my favorite quotes is DaVinci: “Simplicity is the ultimate sophistication.” This certainly holds true in the world of single ended amplification.

Why DIY over factory produced amps?

I like DIY amps because they are made with more than money in mind. They are usually someone’s personal project, built for personal reasons and invested with care, and not built with a sale price factored in. Sometimes they are cost-is-no-object items, employing the very best parts available on Planet Earth. No factory can afford to do that, as further markup puts it out of reach of most anyone. So, with a few exceptions, if you want an amplifier built with the very best parts, you can build it yourself, or buy one built by a hobbyist.

Another factor here is karma. It may sound silly, but the love and attention put into an item built by someone who really cares, versus an anonymous factory worker putting in their 8 hours…it can be seen and heard. Sometimes the amps can be rough around the edges, and occasionally one has to wonder if the thing is even safe to plug in (!), but in many cases the end result of a hobbyist's efforts is an item of such character and quality that it is beyond reproach. In most cases it is the only one out there, a unique item often built around a tube or circuit far off the radar of the mainstream. DIYers usually don't make the same amps again and again either, so you can own a handcrafted one of a kind item. Factory built amps made to fit a price point simply can’t compare.

Triodes vs “other” tubes run as Triodes

Triodes are lovely tubes. The real triodes all have a special fullness and richness to their tone that is highly addictive. They come from another era, when your grandparents were young and the world was a simpler place. Each of the triodes has its own flavor, the 300B sounds different than the 45 for example, but each is really something special when run in a well-designed circuit.

The Type 71A is the baby of the triode world. Dating from the mid to late1920’s, its one of the oldest triodes, and is the fore-runner of the legendary Type 45. In a single ended circuit it puts out ¾ of one watt of power (750 millivots!). It takes a special speaker to do this tube justice, but it has a very articulate sound and warm tone, as well as something very special in its ability to provide a sense of space, making it well worth a look. Within its limitations, it is one of the best sounding tubes I have heard, and one day I intend to own a no-holds-barred amplifier based around this awesome tube. Early globes are still available and affordable due to lack of demand. The later ST shape is also a great tube, with a bit more punch but slightly less space. This tube fell out of favor long ago and is definitely on the outer fringes of tube amplification.

The Type 45 is one of the best audio tubes of all time. Beginning production in 1929, its still available in the wonderful early globe shape that ended production in the early 30s. The ST shaped 45 remained in production until the 1950s. The 45 is a very rich and detailed sounding tube, with good bass, good treble, amazingly palpable tone…its all there with the type 45. At 1.5 watts per channel run single ended, this tube does still demand efficient speakers, but I feel that this may be the ultimate triode. New production tubes by Sophia, EML and others mean that this tube will be in the audio world for a long time to come.

The Type 46, while not a true triode, was apparently meant to be run as one. Much like the 45 in shape and very slightly bigger in size, the 46 dates to the mid-1930's. A very fine audio tube, its one that's off the radar a bit and you dont see many amps built around this tube. It's sound, in the one amp I've owned, is much like the 45 but maybe a bit more euphoric. Good bass, great tone, lots of image if it in the recording. I like the 46 a lot. NOS-testing tubes are still readily available thankfully, because no one is ever going to put this tube back in modern production.

The 1626 is an interesting small triode, and has come to be known in the hifi world as the “Darling”. Available only in the ST shape, this one was used as a ship to shore and ship to ship transmitter tube in World War 2. Like the 71a, it puts out a lowly ¾ of a watt, but unlike the 71a, the amps I’ve heard all have a good bit of bark. It's a very rich sounding tube with a ton of detail retrieval, and a quite appealing low cost from plentiful new old stocks dating back to the 1940's. These are super "musical" tubes and one of my all round favorites so far.

The 2A3 is the big brother of the 45. I have very little experience with this tube, but can say that it puts out about 3 watts in most circuits and is a legendary triode. It has a great reputation as a hifi tube and because of that prices for the best NOS tubes have really gone up in the last decade (single plate tubes for example command astronomical prices). Like the Type 45, the 2A3 is in current production by a number of tube makers, so it is not going anywhere soon.

The Type 10 is one of the best sounding tubes I’ve yet heard. Its available in early globes from the 1920s, as well as the later ST shaped bottles, and has a number of designations; 10, 10Y, CX310, UX210, VT25, etc. In my experience, the early globes sound best, but they are very fragile tubes and easily broken in transit. The sound of the 10 is extremely clear, but it still has a wonderful richness to its tone that is very satisfying. Most type 10 tubes have a thoriated tungsten filament, which glows very brightly when running, making the tube almost a small light bulb. Certainly one of the best audio tubes out there, it's still an outlier and you don't encounter many amplifiers based around it, in part because it requires rather unusual transformers. This tube is occasionally used as a driver stage in some more elaborate circuits. With Elrog bringing the thoriated tungsten filament back to life in their version of the 300B, one could hope that the type 10 globe might be resurrected some day in the future, as unlikely as that may have seemed just a few years ago. Lets hope so, its an amazing tube.

The 300B. Probably the most famous of the triodes, Western Electric still had these in production until the mid-1980s. A large and robust tube, this triode puts out a hefty 6-8 watts per channel in a single ended design, making it very speaker-friendly. Original production Western Electric tubes are universally regarded as the “Holy-Grail” and prices for these tubes have hit outer space. In current production by a number of companies today, it can be found in many forms, with many variations including globe shapes and mesh plates (and now even a tunsten filament), none of which are true to the original. I have a love-hate relationship with the 300B. It can be a very fine sounding tube, but its prices make that fidelity less appealing. Many other tubes sound as good or better than the 300B and cost far less (the 13EM7 kicks its ass all day long for $4-$6 a tube!). The 300B does have an extremely appealing liquid midrange that can be intoxicating. Every audiophile should hear a well-implemented 300B amplifier at least once, it's the standard.

The AD1. This is a triode I was unfamiliar with until I ran across an AD1 amplifier built by Sean Casper. It's a European triode dating to the 1930’s and is sort of the European equivalent to the 2A3. It's the pinnacle of triodes in some ways and was only made in small numbers just before the Second World War. After the War a few industrial versions of the tube were made but all in all this is a scarce one, and prohibitively expensive. So how does it sound? Magnificent actually. Warmth, tone, space are all so good, and effortless with the AD1. Surprisingly (to me at least) Emission Labs has recreated this tube so it seems like it will be available for the time being at least.

There is another class of triodes that I have no experience with; the big transmitting tubes. The 845 is the one seen most often, followed by the 211, but there are a variety of others, and some are quite exotic. Most put out a good bit of single ended power, figure 18 watts or more, but they also put out a lot of heat! And the voltages in these amps are enough to make one pause. Not for the faint of heart.

Pictured above is a representative group of triodes. From left to right: 1920’s Tung Sol 71a globe, 1930’s Champion 71a ST, 1930’s Sylvania 45 ST, 1930’s RCA Radiotron 46 globe (not a true triode but included here just because), 1920’s Cunningham CX-310 globe, 1940’s Hytron VT-62 (801a), modern production Electro Harmonix 300B, 1940’s RCA 1626 (the Darling).

Here is perhaps the greatest triode of them all, the mighty 45. Pictured here, from left to right: 1940’s Sylvania 45 ST, 1931 Ken Rad 245 globe, early 1930’s Perryman PA-245 mesh plate globe, modern production Emission Labs 45 mesh.

The amazing 6L6

So, all that said, triodes are not the be-all-end-all. Great performance can be had from a wide range of other tube types when wired as triodes. This is true of EL84, EL34, KT88, and many others, and many of those choices provide far more power than most of the true triodes, making them easier to own and compatible with a much wider range of speakers. In particular, I’m a fan of the 6L6 tube. In continuous production since 1936, the 6L6 tube has the longest active lifespan of any electrical component ever made, and that's not an accident. I’ve had a number of 6L6 amps in and out of my system, both single ended and push pull, and always find they have much of the real triode sound, but with a bit more grunt, a bit more oomph, and a much nicer price tag. The 6L6 is such a great family of tubes, in part because of the huge variety available. The 6L6 is also an 807, 6BG6 (my personal favorite), 350B, KT66, etc. The list goes on with some incredible military tubes by Bendix, Cetron, and Tung Sol (the 6AR6 is really something special). So in short, don't be put off by “lesser” tubes run as triodes, they are well worth a look and there is nothing “budget” about their sound.

All of the tubes above are in the 6L6 family! They are (from left to right and back again) 1950’s RCA 6BG6, 1950’s Sylvania 5933, new production Gold Lion KT66, new production Gold Lion KT77, 1952 Tung Sol 6AR6, 1940’s National Union 807, 1940’s National Union 6L6G, 1980’s Russian OTK 6P3S-E, new production Tung Sol 5881, new production Sovtek 5881/6L6WGC, 1960’s Siemens 6L6, and new production Valve Art 350B. All of these tubes are great audio tubes, and several of them are flat out superb. The 350B is a great tube by any measurement. The 6AR6 and the 6BG6 are two of my favorites, as stated above. Both require a pin adapter, but are otherwise plug and play with most 6L6 circuits, although the 6AR6 has a low screen voltage requirement. In most cases, a full quad of any of the tubes above could be purchased for less than the price of one boutique modern production 300B tube! And in a well-designed circuit with quality transformers, many of these tubes will outperform a 300B. For me, this is a good example of the rapidly diminishing returns associated with some of the high-end audio world.

A small metaphor for the sonic differences of tube types

I feel the video below is a kind of metaphor that illustrates in some ways the differences in the sonic characteristics of tube types and amplifiers. The video is of guitarist ‪Marcin Dylla playing Tбrrega‘s Capricho Arabe on six different guitars‬. Some are vintage instruments while others are more modern. All of the guitars are of course superbly crafted works of art, much like many of the amps that I’ve owned. In this performance, with each guitar seamlessly woven together into the same music, the differences in presentation between the six instruments is clear. All sound excellent, but different. I was struck by how much this resembles, for me, the way a type 10 tube sounds different from a 45, and so on. At any rate, at the top levels of amplification these are the differences you can expect rolling the audiophile dice on new gear. With the best amplifiers (and tubes) its rarely night and day differences, but often subtle flavor variation. It took moving a lot of stuff through the doors to get that one through my head!

Mr. Dylla gives a very fine (and well recorded) performance of Capricho Arabe.

A few words about Vintage Audio

I love antiques and old stuff, and that's part of what drove me to become interested in tubes and tube audio. I’ve played around with both new and vintage audio and have to say that the older stuff is better in general. I don't know if it's the materials used (some of which may be forbidden now) or the workmanship (which is almost always superior), but the quality of sound from older pieces is something I’ve noticed again and again. For that reason I’ve developed a clear preference for vintage transformers, older alnico drivers and of course NOS tubes. That's not to say that new tube audio gear is not good, some of it is truly excellent, but to be on the safe side I’d always choose a newly made amplifier built using vintage parts over a newly made amplifier built using new transformers and tubes. In my experience, the older stuff often has a sizzle and snap that the newer gear just doesn't make.

Happy listening, and thanks for visiting my page.