There are certainly new tube amps that are not shy about announcing their obvious and unchanged lineage. But, I suppose it mostly depends on the design. Generally speaking, circuit design and parts quality have changed enough that today's gear is bound to sound different. Even an amp using the same schematic as a Dynaco, but, made with today's parts will not sound exactly like a vintage Dynaco.

There are plenty of new amps that sound nothing like vintage amps; it seems that tube and solid state amps in the upper echelons probably share more in their sound (or rather lack of) than ever before, from what I've heard and read. Convergence is inevitable as you approach the sonic ideal of "straight wire with gain".

Tube design has moved right along with everything else. Consider the use of the Russian "super" (6H30) tube in a lot of preamp or Conrad Johnson with all the trickle down technology from their ART (Anniversary Reference Triode) preamp. How about OTL (output transformerless) amps from companies like Transcendent Audio? Gear like this shows that tubes and tube technology are not obsolete but still advancing.

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... given the apparent stagnation of tube development ..

Well, I guess if you assume that tube development is stagnant, then you won't know much about what's happened in tube development over the last fifty years. However, if you read the reviews of the modern tube equipment, you will see there are plenty of new innovations in tube circutry. And not just in the quality of parts uitilized. Read a few articles to see the innovative ways designers are approaching tube circuitry.

http://stereophile.com/tubepoweramps/606moscode/

http://stereophile.com/tubepreamps/305cj/

http://stereophile.com/phonopreamps/935/

Tube based pre amps are quite innovative in how they build a circuit and the ability to hybridize the circuit only makes tubes more innovative than ever before. The use of Nu-Vistas by Musical Fidelity offers "new" tube circuitry that hasn't been touched for over forty years. New tube types are still being developed (KT-90's) and even old type tubes are given new life in new circuits and with better than ever build quality. Forty years ago it was almost unheard of to buy a phono pre amp that didn't rely on 12AX7's. Now you can choose from numerous tube types that suit the purpose of the designer and listener. Or you can buy a phono pre amp based on a circuit from the 1930's with a single dual triode tube.

Tube based power amplifiers mostly fall under the umbrella of UltraLinear, Unity Coupled or Williamson. Unless they are single ended triodes based on designs from the first half of the last century. OTL's are old news also. But the way the circuit is built around these basic building blocks constantly changes. Read the Moscode review for more of an idea what I mean. The simplicity of most tube circuits has many people thinking not much changes with tubes. There aren't many parts in most tube designs compared with solid state. So, just what can a designer change?

What has drastically changed is how the transformers are wound. Tube based power amps rely heavily on the quality of their transformers and today's computerized winding facilites make many transformers as well as the revered hand wound units from the past. But new laminations and winding methods keep one transformer from being just a replica of another. New power supply designs and biasing schemes are constantly being used in new amplifiers. The power bandwidth and square wave performance of today's best tube amp is far better than the average tube amp of forty years ago, due largely to the performance of the transformers. Yet, one of the most respected tube manufacturers of the Golden Age has their MC275 back in a class A slot of recommended components. Go figure!

Tube gear has marched steadily forward after more than one hundred years of design. Unfortunately, solid state design has stagnated after only thirty years as most non-tube designers have shifted their attention to digital techniques and consider analog solid state a dead field.

As for the transformers that Jan is speaking of he means the output transformers. The advances in computerized winding techniques has made a real difference in the sound. OTL's don't have any output transformers so its circuit design and parts quality that make the difference with them.

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The quality of the transformers, both power and output are the heart and soul of a transformer coupled amplifier. In the Golden Age the person who could create "hand wound" transformers was the equivalent of the mechanic who could tune side draft carburetors and adjust valves by ear. They were Gods. There is a simple reason good transformer companies made good audio companies. Arcosound gave way to Dynaco and the best transformers to use when rebuilding a ST70 are still the original models from Dynaco. http://home.indy.net/~gregdunn/dynaco/history.html

Marantz and McIntosh thrived due to their transformers and Mac still uses autoformers in many of their designs to this day. Since the amplifier begins and ends with a transformer, the quality and implementation of the transformer design makes or breaks most tube power amplifiers. Power transformers that leak RF radiation or hum at all volumes are going to affect any amplifier, tube or solid state. Bandwidth, square wave response, saturation of the core and distortion product, etc. are all affected by the quality of the transformers. They are the impedance matching device between the high output impedance tubes and the speakers. Get it wrong there and you've lost everything. In short, there are "audio grade" transformers and then there are "audio grade" transformers. A lousy circuit with a lousy transformer is a lousy amplifier. A top notch circuit with lousy transformers is still a lousy amplifier.

As far as NOS tubes are concerned, you are confusing tube manufacturing with tube amplifier manufacturing. The amount of tube manufacturing plants has steadily decreased over the last forty years while the number of tube amplifier manufacturers has steadily increased. As demand for quality tubes shrank in the 1960 - '70's, the tube market was primarily made up of musicians who used tubes far longer than consumer audio users would consider worthwhile. With the resurgence of tubes in the late 1970's, tube manufacturing began a slow but steady comeback though the number of tube production plants gradually decreased. Most plants in the US and England were too far gone into disrepair to be salvaged by that time. Plants have been moved to foreign lands and production has continued on with many of the original production facilites being used. The economics of tubes is a strange item that has involved underworld/political connections and forced buy outs. Plants are in business one day and sold to another owner the next. New tubes are being manufactured in both Russia and China with both countries building tubes that are similar to the originals made in the US and Britain decades ago. As the number of NOS tubes continues to dwindle, new tubes are coming on line to take their place. Some of the new tubes are close to, or slightly better than, the original NOS tubes. New tubes are getting better all the time. But, that doesn't mean you can buy any tube and have a good product. Keep reading Stereophile to keep up with developments in tubes. You would seem either not to have been paying attention over the last decade or you would just rather assume tubes are an obsolete technology.

I would guess you are wrong about most tube lovers wanting to go SET. SE and PP have their own limitations and benefits. Anyone who has used tubes for a while should know what limitations they place on their systems. There are fairly simple guidelines for when a SET isn't appropriate. However, like full range single driver speakers, simple designs like SET's make music in a very different fashion. I can listen to SET's driving FRSD speakers and appreciate what I'm hearing. That doesn't mean I want to trade my Mac tubes for a SET amp or my Rogers speakers for a pair of Lowthers.

How long have you been reading about tubes? Have you ever heard a well balanced tube based system?

I'm unaware of any tube amplifier manufacturers who sell their own transformers. There is a magazine published once a year about this time that gives a run down of most companies dealing in vacuum tubes. I can't remmeber the exact title, something like "Vacuum Tube Directory" or something as straight forward as that. You might find it on the bookshelves in your favorite bookseller. Also, you can pick up a copy of "AudioXpress" which is a DIY oriented magazine. There are lots of ads for tansformer companies in there and articles detailing DIY tube amplifiers. Also, look through this web site; http://www.worldtubeaudio.com/

Will your DIY sound any different than a commercial product? I don't know. First of all, I don't know how keen your ears are. Secondly, I don't know how you feel about the ability of passive parts to influence the final outcome. I'm not sure where you plan on aquiring a schematic for a commercial product nor how well you can translate a schematic into a working product. Some are available on line, but these are mostly older designs. VTL has published several of their designs. Most lack a power supply schematic and since an amplifier is a modulated power supply, what you do with the PS will affect the final outcome. Many commercial companies have proprietary windings for their transformers though you can certainly get a good transformer from a reliable source. I would pick a DIY project and try that first. If this is a one off, build your amp to save some money project, then I wouldn't try to copy a commercial product. If you are doing this to learn about tubes, then trying a DIY project and learnuing from that experience is more valuable. Even if you don't care for what you've built, you tear it down and start on another project. You can build from a kit, of which there are many tried and true designs; http://www.bottlehead.com/ Or, you can build from a schematic, of which you will find many on the World Tube Directory site or just plug "DIY vacuum tube amplifier" into a search engine.

AlexO - My guess is it's very likely you would end up with different sounds. Take a look at the following page and all the variables that go into designing transformers:

http://www.geofex.com/Article_Folders/xformer_des/xformer.htm

Throw in different lengths of wire, wires with different insulation and even a point to point design will have different properties and sounds. If the amp has a circuitboard, signal paths, lengths, and how the traces are routed will affect the outcome (routing of traces can affect noise, RF & EMI susceptibility.) Choice of resistors, capacitors, and diodes will surely make a difference. All those little changes will add up and make differences in the outcome. It would be an interesting experiment to give 2 people a schematic and have them build amps to compare.

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Wouldn't they all sound more or less the same with the only difference being in cost and perhaps the chassis?

That idea leads us to the basic argument of parts is parts. Therefore, don't all amps sound alike? And, once again I have to fall back on the basic question; how keen is your hearing? Certainly we expect two similar amplifiers from the same company, let's say two McIntosh MC501's, to sound essentially the same. But Mac doesn't sell its Unity Coupled transformers. So creating the same piece of equipment with off the shelf transformers modelled after Mac's design puts us at a disadvantage before we start building. How close would our DIY amp come to modelling the Mac's sound quality? If we carefully assemble a duplicate with only minor variations, probably only minor variations would exist in the final outcome. Whether they would be enough to convince you the result was worth the effort would be a matter of how intensely we listened.

You don't find many DIY'ers duplicating commercial amplifiers. Copyright and intellectual property and all that. Plus, most DIY'ers who build from the ground up want an amp they can call their own. Your phrase, "if they use the same design" misses the point of high end audio and DIY. If there were only one design, or even a few designs, that were worthwhile, every company would be building the same amplifier. That DIY'ers take a commercial amp and then modify it to suit their needs is an example of even accepted designs not meeting some folk's desires. While there are many amplifiers that would appear similar to a ST70, most have some variation that makes them unique.

So, I guess my answer to your question would be, yes, I suppose you could come close to duplicating the sound of the original product, if you could put together all the pieces the original manufacturer used. But, I doubt that it would be worth your money or time. This is somewhat like asking whether or not you could build a 1969 Z28 Camaro from off the shelf parts. Yes, but it will cost you $100k. And who would want it besides you?

Manufacturers deal in case-lot quantities and multiples of production to lower their cost. The one capacitor you would buy to build this clone will cost you at least 25-50% more than the manufacturer pays for a 1,000 piece-lot of the same capacitors. Multiply that by 40 capacitors you will need for one amplifier. Do the same for all the other passive parts. The tubes will cost possibly even more since many high end manufacturers burn in and test the tubes they use and reject a fair number as out of spec. (You can pay for this matching to be done at the retailer, but then you've raised your cost once again.) If you don't have the test equipment and knowledge needed to troubleshoot any problems, who are you going to turn to? Are you just going to trust that everything went well and hook it up to your speakers without testing it first? I doubt any repair shop would take in your clone and try a repair on a piece of equipment that might not be wired correctly. Or just wired without the correct color codes for internal wire braids. Can you buy the wire used by the company in small enough lots to buy six different colors of insulation? You'll probably have to buy 50' spool of each color when you only need two feet of each color. If you can't buy a proprietary wire, does using the same internal wiring matter to the end result?

In the "olden days", more than a few companies sold their products as kits to a burgeoning audiophile community eager to learn about electronics and audio. And a homeowner eager to have a clone of their favortie amp at a bit less than retail price. Finally, these manufacturers stopped making kits because of the problems associated with the inexperienced constructor who had one cold solder joint among a few hundred in the amplifier. That one cold solder joint caused intermittent problems or caused the amp to simply not function. Many kit amps were left in closets due to cold solder joints. If you are looking at a used Dynaco ST70 today, you are still advised to steer clear of the old kit built versions of the amp since they might have bad solder joints that will cause problems unless you completely strip the chassis and start over. There are more than few arguments against building your own equipment.

Finally, let's say you have built the amp and found it satisfying but you want to move on. Who is likely to buy a one off clone of a Mac MC501? You will have virtually no resale potential. Add all that up and there is very little reason to try to duplicate a commercial product.

If you are intent on building something that was once a commercial product, I would pick something like the aforementioned MC275. A classic Mac amp that is now occupying a class A slot in recommended components, the complete schematic for the original is on the web. You can pick up used Mac transformers from several sources. You can probably even find a junker chassis with transformers and start rebuilding with the real thing. Replace all the parts and you can have a Mac MC275 that you built yourself. Chances are it will sound very close to what you would buy today. Of course, the parts are going to run more than buying the amp new or in excellent condition used. But, you will have completed your desired mission.