· Take the VK-50SE Guided Tour!

As an enlightening exercise, one could approach audio designers with the following question:

If you had a magic wand and could construct your ideal or "dream" amplification device - what would it look like?

Unfortunately, as audio designers, we all have to work with real, not imaginary, devices. We constantly look through catalogs, both old and new, solid state and tube, in an endless search for the best. We never find that mysterious device of our dreams, but we find some that come close in certain areas of their performance envelope. This transistor might fit our expectation in the area of its on resistance, this tube has superb transconductance, and so on. However, all real devices are inevitably compromises, so often to get a good parameter X, one has to sacrifice the parameters Y and Z. Life was never meant to be easy for audio designers.

Of course, the definition of the "dream device" also depends on the task at hand. Are we designing a line preamplifier, a phono-stage or a power amplifier - each case would call for a different ideal. For the purpose of this exercise let's presume that a line stage preamplifier is our project.

Immediately, we find a four-prong split of designers and their preferences. We have the macho drummers for the Bipolar transistor. We have the gentle JFET folks. There is the silent MOSFET majority. And, of course, we have the religiously fervent Hollow State practitioners - although this last category could be further split into many subcategories: pentodes, triodes, directly heated tubes, indirectly heated ones and so on.

We are not trying to force a decision on which one of these many roads would lead to the best possible line stage performance. We are simply providing one designer's perspective on what his favorite "dream device" would look like. This endless search has led us to an unusual and important discovery.

The job of the line stage preamplifier is thought to be simple. It take in the signal in an easy-to-handle (so anyone can do it) range of around one volt and amplifies it by several times, ten or so will suffice in most cases. In fact, in many instances you don't amplify at all, you actually reduce the signal.

The usual design requirements for a line-stage remain, things like comfortably high input impedance, low output impedance, low noise, wide frequency response and a volume control that doesn't degrade the sound.

Just one look at Balanced Audio Technology's products will reveal much about this designer's preferences:

Triodes No cathode followers No overall negative feedback Plate-loaded low-impedance circuits High current operation Medium gain (15dB to 20dB)

Based on these preferences, what "ideal" device would we like to see?

1. A vacuum triode.
2. An amplification factor of 15 to 25.
3. Very low plate resistance - 100 Ω or less - the lower the better! No buffer or cathode follower should be required when building a simple plate-loaded circuit.
4. High transconductance for low noise - in the 250 mA/V range.
5. Filament current of 10 µA - we are dreaming, aren't we?
6. Miniature size.

Needless to say, no tube with these performance specifications shall ever exist. We, therefore, continue the search for the best available alternative and adapt it to our design requirements.

We could cut to the chase and declare the obvious: among the readily available tubes, the one that comes closest to our ideal is the ubiquitous 6922. It offers a balanced combination of the ideal parameters and rightly finds its place in many fine products, including Balanced Audio Technology's own preamplifiers. Perhaps the finest application of the 6922 today is the mighty twelve-tube VK-50 - a design that may very well represent the ultimate in what this proven amplification device can deliver.

Nonetheless, to continue our quest toward even better sound and still higher performance, we acknowledge that the 6922, as great as it is, is still far from ideal.
What we need is a new device with a set of characteristics that seem as yet unobtainable. We remain diligent in our search.

Fortunately for us, somewhere deep in the belly of the former Soviet military machine, life never stops and never gets boring. There are new threats, both real and imagined, developing every day. New performance goals. New designs on the drawing board and new Party leaders to keep happy. So what that the West had abandoned vacuum tube technology decades ago! Some still kick themselves for doing this prematurely. Tubes, after all, can do certain things far better than solid state devices. So, keep your slide ruler sliding, Comrade, never mind that calculator, and give me some totally new devices to work with, something to really get me going, something the likes of which the West has not yet seen and quite possibly never will.

Many years ago, the Soviet engineers designed the tube that is now the high-end audio industry standard and mainstay - the Russian 6922. Of course, back then they used to call it the 6H23P, just another member of the growing "H" family of small dual triodes. It is a good tube to be sure, and specifically designed for cascode operation, low noise, relatively low plate resistance, wide frequency bandwidth, and low filament power requirements. But the restless military puts even tougher tasks in front of their design teams: the enemy never sleeps and progress must continue marching forward. Here is a proposal sheet for a new device with a combination of parameters that no one in the world has yet seen. But no, it is not possible, no one can build a device like that, so please go away and don't bother us!

The generals, however, do not relent. So the most capable team - electrical engineers, materials scientists, and technologists - start their work and years later, behold, the marvel is born. It is given the official name 6H30P. Its existence shall remain unknown to the rest of the world and it is officially banned from export. Its intended application shall remain secret.

East is East and West is West, but with the fall of the Soviet empire the twain do meet. Through such advanced communication tools as the Russian grapevine, Balanced Audio Technology was able to learn about the quiet existence of this device. But it is still cloaked in secrecy. Even with the Iron Curtain having rusted away, it remained completely forbidden for export, so dear was its performance to the Russian military. There is no analog to it in the West.

Nonetheless, we were able to obtain a few samples and our marvelous VK-5i was modified to accept them. The trial results surpassed all our expectations. The 6H30P proved to be better than the 6922 in virtually every respect - whether in its measured performance, or more importantly, in the quality of the resulting sound. From that moment on, our goal became clear - to obtain this new SuperTube and bring it to the West for use in our flagship products.

It took great effort on both sides of the Atlantic, but we are happy to report that Balanced Audio Technology now has the exclusive rights to this device. The 6H30P tube, branded with the Balanced Audio Technology name, is making its Western debut in our first Special Edition product - the VK-50SE. The VK-50SE balanced line-stage preamplifier was designed from its inception to be a platform worthy of this tube's potential. Together they fuse into a combination that is truly greater than the sum of its parts.

No, the 6H30 SuperTube doesn't meet all the performance criteria set forth for our dream device. It does, however, substantially close the gap between that distant dream and today's industry standard - the 6922. In very simple terms, it triples or quadruples all the "goodness" of the 6922.

The VK-50SE relies upon eight of these marvelous devices to achieve unparalleled performance. Using our proprietary Unistage® topology (first introduced in the VK-5 in 1994), we effectively create a device with these unprecedented parameters:

The simple differential plate-loaded gain stage in the VK-50SE now sports an output resistance of 200 Ω per phase and load current delivery of 65mA. As usual with Balanced Audio Technology products, this is done with no buffers, no cathode followers - and only a single gain stage. Just like the Single Stage to Orbit space vehicle that NASA is working on, it launches the practical application of tube technology to a new high.

One listen and we're sure that you'll agree.