Sunday, 24 December 2017

Faith, Hope, Salvation - The Single Ended Tube Amplifier

Hi everybody,

since a long time I didn't post any article about tube based audio with vintage components. To my understanding almost everything substantially was said within the last four years about this topic. But now here I will try to bring right in time a known Christmas fairytale with some new accents.
In particular after my series of articles about the rise and reintroduction of tube amplified audio with a synonymously way to create the Western Electric 300b tube as central element of religous passion over the last 30 years. Yes, a vintage Western Electric 300A or 300B tube is a exceptional unique sounding device with unparalleled attitudes – period. But a lot of other triodes like the 45, the 2A3, the 6BG4, the RE604, the R120, the AD1 and several other directly heated tubes from that period before the 1950ties (i.e. mass production) are as well unique sounding devices, each with a recognizable fingerprint soundwise. Not even to note the big bottles 211, 845 and GM70.

To keep the example of the WE300B, there are more than 10 different vintage original WE types known, which show all the originating imprint Western Electric, made at different production places and in periods from 1928 to 1998. Further are additional license productions, like the well known Cetron or the STC 4300B (Standard Telephone and Cables, GB) versions. Each of this different 300B tubes show a clear and comprehensible sound attitude, different to any other sample of this types. The reasons for such might be today found in aging, storage conditions and of course, even in little production differences and materials. Tubes are made to technical given standards and the most of us know, technical specifications can be evaluated through measurements, but sound cannot. This insight brings us to the question if automatically a more rare and a inevitable more expensive tube is generally the better sounding device?

Three WE300B tubes, one from Cetron

For some, who might fire their barbecue with 100 dollar notes, the permamently rising price tag for vintage WE 300B tubes might be neglible. Dripping every day 10 dollars into the money box is the value of using vintage 1950ties original 300B tubes for some hours every day. The latest Western Electric originated 300B production from the 1980ties generates price tags of 2500 $ for a NOS pair, a used single graved base tube from early production will cost a good 3K$, New Old Stock asks for a open range between 10k and 20K$ for a 70 year old pair. Yes this tubes might do sound exceptional unique, hardly to compare them to any later production line, but do they really sound that much better than later versions,  – or just different? Or does the price tag create a very special cognition, which tricks psychologically our auditive perception? (a common sign of market religion) How long will such investment work, yes 70 years ago such tubes could fulfill the WE specifications of 10000 hours minimum service, but what happened in the meanwhile with such tubes? How do they have been stored for the major past time, nobody can tell you here some reliable truth. Recently I did make a lot of tube testing with NOS tubes from the 1940 to 1950ties production period. Top NOS products from GEC, STC, Mullard/Osram and others have been on test. From every 10 piece batch two tubes failed within shortest running time without recognizable reason. I have never listened to a very early produced WE300B tube, I can remember a shoot out between 1950ties and 1980ties production lines and as a third contender a Cetron type from 1970ties production. This shoot out happened a good decade or longer ago, the oldest tube showed up with the darkest, deepest and widest spread sound attitude (or was it just almost gone?).

Today, if you want to buy a new made tube (new for safety reasons, i.e. religion again, when talking about Chinese tubes, I remember my first bought chinese 300B tube ever pulled out of a box in 1992 failed with a first switching), you can get modern replacements made from China, Russia or from the former East production. This modern tubes do sound substancially different than the most of the vintage original products,  – to say it carefully – the most of them does sound infected with cough or hoarseness, without any elegance and tonal refinement, which is so typical for vintage production tubes. To say it straight, they are absolutely useless, if you you are hunting for a three Michelin star graded audio dinner. In deregulated markets the price tag does not reflect any quality aspect, today its more going to be visa vice. In price ranges between 200$ up to 1000$ for a pair of modern 300B bulbs, you will have today a wide range of choices to get the mechanical value of a ordinary electrical light bulb. It seems to be still a good terminated business, to keep the religion running by serving such tubes to people of the 300b-faith congregation. Captured that only 300B tubes can do the trick, people spend still astonishing amounts into such wearparts, driven by the hope of audio salvation. (typical phenomenia within altered capitalism as religion?).

My long term compaignon power amps, the legendary Leak TL 12.1,
one of the finest push-pull amplifiers in history

Comming back to the essentials of this story, the rise of the 300B tubes was on par with a fresh reconception of the Single Ended Amplifier in the 1980ties. This topology can show some exceptional attitudes and advantages, comparing their merrits with other tube amplifier design principles, like the classic push-pull-designs, known from uncountable variations in the longer past, which are based on D.T. N. Williamsons article in Wireless World 1938, the so called the Williamson Amplifier. All the derivates do use pentodes, tetrodes and their kinkless relatives in order to generate a powerfull output of 12 to 100 watts, with theoretically improved distortion figures. Some of these amps, in particular the very early examples do sound exceptional good. The most of the crowd sounds like what is today known as "tube amplifier sound". Dynamic, a bit cheeky, but mostly impressive. The most readers here know my long time relationship with a better example, the early 1949 Leak TL12.1. These push-pull amplifiers are rediculously overenginered in several aspects and they do sound exceptional transparent and natural, I could not find in 30 years of evaluation something from other manufacturers, which was even close beside. I got once a really early set of Williamson Amplifiers, built in 1950ties from a british radio engineer in Bristol, realized at the best possible level of parts and manufacture. Made with Partridge and Parmeko iron as four chassis design (PSU and amp chassis in double mono), these amps are very close to the Leaks, if not on par. Once I will do a own article just about this incredible realisation as piece of important audio history. Both amps use the KT66 from GEC as power output tube, a tube which was designed around the same time of the Wireless World article. The Kinkless Tetrodes KT66 from GEC are the summit of such pentodes or tetrodes in the 25 watt class. Almost every manufacturer of this time did make a own design, RCA began with the 6L6 as base for all of them in 1936, Mullard/Osram did the EL37 in the late 1940ties, another derivate was the US-designed 807 and 5881. In these days a lot of different applications got as well designed, so that the demand for such tubes was immense. RF-amplifiers, military or civil rf-,  radar-, pa- and tv-stage-amplifiers and finally der growing audio and music business created a huge market for such tubes. In the 1950ties almost every manufacturer in in GB had a luxury power amplifier with KT66 in their portfolio, since US-american makers mostly relieed to 6L6 tubes in these days.

Original bochure from Wireless World about the Williamson Amplifier from 1951

These original tubes are mostly exceptional good sounding tubes when compared with modern reissues, mostly made in Asia. So its is understandable that a new old stock quartet of GEC KT66's today will cost almost 1000$ or even more. Everybody who has compared these tubes with any modern variants, even if they look completely identical, is willing to pay the difference of almost 850$ to get the real addictive drug for his guitar or audio amp. If you own an amp which is able to show all aspects of such refinement in sound quality, like with a magnifying glass, than you know that these tubes can do a unparalleled job for you. This is a alternativeless lessons of truth with push pull amplifiers, but it is even more important with a single ended amplifier topology, where only one single power tube is the decisive key element for its finalized sound. Beside the used iron, which is quite important, but in its role for the realism are transformers highly overated, the power tube is a key component.  If you don't believe about, just have a look to the "legendary" output transformer of the even more legendary Western Electric 91A amplifier, the WE171A transformer, which is a small and lightweight piece of iron. In its days almost any signal was limited to a frequency range of 200 to 5000 hz, in cinemas intelligibility was the major demand, speech frequencies between 500 to 4000 hz was the aim of audio designers. This range is what the "legendary" Western Electric amp shows as its best attitude, such performance is even by todays standards a exceptional result (look at the WE aficionados running wide band horn systems with this sort of amps to match their middle frequency performance).
But today the most of us prefer some high end audio quality, let us point it out, a fast, undisdorted and lean low frequency response from 40 to 100 Hz, or even deeper with powerfull liquid distributed dynamic energy output. The frequency extremes are not the foremost attidude of the legendary vintage amps/i.e. its output  transformer/ i.e. the foremost domain of the 300b tube, it was never intended to be so. The wonderful middle frequency response of such amplification with original 300b tubes, was the point which made this combinations legendary once in the early 1970ties in Japan. They got a synonym for a different realized audio response, which is hardly found in much more technically elaborated products from the second half of the 20th century, not to talk about all the contemporary products, which are just feeding only a remnant  theoretical demand of audio, or let us say it in more straight words – religous belief.        

This article aims to those who have not yet come under wheels in their individual sensual independence and are still able to differnence out on a base of personal auditive ability. Those who want a more natural and less technical sound quality, those who do not want to make some drugdealers fat, those who do not want carry on the misleading message, – for those I have some good news. All others who want to consolidate and follow some tribal paths of gone history, religous correlations or faith congretations with different color codes, from black to grey to green, can stop now reading!

Rebuilt from Cary Audio Push-Pull 300B stereo wrack. The stereo set of NOS tubes from
Cetron, STC and Rogers does cost 50 $, together, not one tube!

In 1994 I did buy a already completely slaughtered 300B push pull amp from the than emerging US-company Cary, which was in these days to my knowledge, the only American manufacturer of single ended amps in the US-market of higher faster further audio. With typical sales arguments of extreme heavyness, glossy shine and solid stainless steel cases this company marketed a range of different 300B amps in the US and as well in Europe, as the one and only salvation for the new tube age in these days. Single Ended mono blocks with one 300B or as Parallel Single Ended versions with two or like this example here, as Push Pull Stereo model. I can remember that these amps were quite expensive, all between 5000 and 15000 $US, which was good money in 1992. So I was a bit astonished to see a eviscerated example for some 50$ at a final outsale of a closing local hifi-shop. This amp was completely emptied, without any wiring or components, but with all original hardware. The shop owner told me that several people tried to convert this amp to a singing bird, but all had given up after a while. The former owners loss was going to be my win. (market religion again) I always had the inherent problems of this amp in my mind and so my idea to bring this thing back to another life, was hold back for years. Alone the investment for four Chinese 300B tubes always suffocated my energy in a glance to start some restauration. It got forgotten in my cellar for more than 20 years til I decided in 2015, maybe to do something with this wrack. First I removed the original output transformers and sold these on Ebay for 400$ back into the US. I stripped it down to the clean chassis and found under the massive casted Cary decal at its front the inscription "6L6-push pull power amplifier". So I realized Cary did manufacture with identical hardware a classic 6L6- and a 300b-push-pull amplifier without change. Now I did understand the amount of tube sockets, the layout was dedicated to a classic design with a half 6SN7 as driver stage, another 6SN7 as phase splitter and two power tubes, all served by a doubled rectifier stage with two 5U4G. With a value of  200uF for the charging capacitor (a lot helps a lot-religion) this amplifier gave me a deep insight into a practice of feeding a new and adolescent market.

In 2016 some friends and I made a final shootout with several 300B tubes (will be reported in another special article once), which showed me again that 300B tubes in audio amplifiers are something for people who don't take care about their money. Maybe the same target group which do barbecue only with the best available hand fed Kobe beef. So nothing for me, I know that the Chianina Beef from Italy is as well a good choice and available for a fraction of the pricetag from Kobe beef. I always trusted in my life into long time established cultural path lines, so I know that in Japan beef got fashionable late in the 1960ties. Before that time beef was almost unknown, because of the lack of pasture, so cows did exist in hand counted amounts mostly in the region around Kobe. (legend building as religion) In the common Japanese kitchen beef didn't play any cultural decisive role. In Tuskany the Chianina Cow has been cultivated for several hundred years with very similar excellent life circumstances for the cows. The right living conditions of the animal and the right treating of the beef is manifested as a several hundred year old tradition which can be read back in the legendary Coquinaria from Martino' Rossi printed in 1465, the first printed cooking book in history. This book was as well a present to the Savoyens, which transcripted that knowledge base for the french cooking revolution 250 years later. I rate Japanese cooking to one of the three best traditions in the world, but to be honest, I never was a friend of the Teriyaki style beef cooking (i.e. cutting beef into bite-sized pieces for the chop stick tradition). The Japenese are better with other things than beef. Have a look at the tv documentation showed once on Arte about the Dashi tradition, unbelievable, than you will know what I mean!

Back to our topic, the single ended amplifier, based on its most famous incarnation, the Western Electric 91A model, is still today a wonderful application as tube amp, but there is no real need to perfom the expensive 300B tubes. A minimalist two step amplifier can show up with a lot of advantages against any other tube amplifier design principle. With other nos tubes such derivate of amp can show all typical attidues on a identical level of audio performance as equipped with 300B's. The most of this attitudes are already common knowledge and have been part of their marketing throughout the last thirty years. Its simplicity is is major win towards refinement, but it doesn't need all the religous writebacks which have been cultivated within this time. Such common fairytales are: 1. direct heated triodes sound better than their indirect heated counterparts, 2. about the exclusive audible excellence of triodes, 3. the second-class rating of multi grid tubes in general as disharmonic element, 4. the over valuation of output transformers for the performance of amplifiers. And finally the witchery as such, 5. the global feedback loop known from conventional designs.

When Maison de L'Audiophile released in 1984 their early interpretation of the original WE 91A amp, their MdL'A300b Legend amplifier with Partridge transformers, showed this reincarnation a very good will to do the best to release a contemporary high graded product of this breed. But it came out with some real faults. Some of these faults relay to time dependend interpretations, like the oversizing of capacitors in the PSU, but some were major faults in the transcription of the original schematic, like a 10 times higher valued coupling capacitor between the two tube stages. Further the far to high valued grid resistor for the 300b tube might be handled by original WE tubes, but several modern chinese copies will be overwhelmed in a glance. About this faults and about the original template Fritz Hunold ( has made several excellent articles. If you aftermath such details and if you ever try to built such an amplifier yourself, you will not believe how important such little changes are, they shift the overall perfomance of such an amplifier together with a precisely adjusted feedback loop from mediocre bastard to world class component. Yes, global feedback! (inquisition!)

Rebuilt with James Audio 2.5/3.5/5K output transformer, Chicago Transformer Co. Choke, three General Electric 8uF/600V smoothing paper caps and two stage nos tubes,

Coming back to my Cary wrack, it showed up with a acceptable power transformer with values for the plate voltage of 350-0-350 volts and with respectable capabilty for rectifier and tube filaments and a stainless steel chassis with 8 holes for tube sockets. A good base for the transcription of the WE91A topology into a stereo (uuhh, another sin – stereo, pah) amplifier. I did reject two giant electrolytic filter caps (600uF) which gave me the space for the James output transformers. The former OPT's gave enough space for a solid nos potted smoothing choke (8H/150mA) from Chicago Transformer Co. on the right and a set of three oil caps from GE of 8uF/600V capacity on the left side. Keep the impedances of the PSU as low as possible!
First important decision for such a simple two step amp is a reliable penthode-input-/driver stage. Where once WE did set the WE310A as a working horse, thousands of copyiest had nowdays better knowledge and prefered here a better sounding triode (religion again. wow, what a mistake!). The penthode is a must to get the full possible swing to the grid of the output tube with only one tube, the 300B is very selective character at this point, but output tetrodes can be similiar. Coupling in tube amplifiers is one of the most important things, I was always convinced about the perfect coupling abilities of transformers for the same reason. So it makes sense to get rid of the phase shift tube stage in pp-amps, but here we don't have such and pentodes make transformer coupling impossible. Here a small coupling capacitor of 0.05 or 0.068 uF (original WE design is 0.047uF) is mandatory and helps the pentode to charge this capacitor easier. (I started  with a typical value of 0.22uF,  which is four times higher and the difference is the same like the sliding a boat or a hovercraft. In order to couple both tubes perfectly and to keep the amp dynamic and liquid in its physical sound structure this detail is decisive) Almost any of the competitors or the successors of the WE310A is on par with this rare and expensive tube. A natural partnering substitude from that time will be the British EF37A/36, VR56 or EF6 such show all a metallized glass envelopes, wich is important to get this tubes hum free. The direct competitors of the WE310A are the 6J7G or C6C, but these can only be run humfree in solid metall shields, or otherwise later made smaller metal tubes like RCA 5693, the complete European noval row EF40 to 89 and similar types, like the loktal C3g are possible. The typical penthode as driver is a must, period. A whole range of power output tubes can be set up without electrical change: the kinkless tetrodes from GEC in the first row, the KT66/88, their high frequency derivates TT22 and KT8c, the Mullard/Phillips competitor EL37 with its HF-derivate EL38, the Telefunken F2A11, American 807, 6BH6 and 6L6 tubes, STC 5B254M/A, Russian 5881s and several more tubes will work perfectly auto biased on point with a 3.5 k-ohm output transformer. Exactlthe same point wich is typical for 300B tubes with a different filament and a different socket. All of these named tubes here are soundwise in such topology extremely delicate sounding sources with slightly different attitudes. When connected as triodes they all do sound certain classes superior to any chinese production 300B's, – period. Each of them has a clear sound destinction, so is my long time favourite, the EL37/38 are more at the transparent side with clear destinction to better detail resolution of the higher frequencies and on opposite side are the typical 807's with a more darker tonality spectrum and attention to the bass weight. Decisions should be made to personal taste and with the speaker attidudes in mind. But prices for such nos tubes are still low, so low that it is very easy to test them out yourself with oktal adapters, which are available trough Ebay from a Taiwan seller. The most of the gang are easy available for 10$ for a nos piece, some up to 50$, only the space deers from GEC, the KT66/88's and the German F2A11s are quite expensive for different reasons (demand, superiority and rareness). It just needs a single ended gapped output transformer from solid audio production made with some reserve, let's say a silicon oriented steel lamination wound for 3.5 K, gapped for 70mA to 4/8/16 ohms secondary, with 100mA capacity designed for a output of maximum of 12 to 15 watts. Such are available from different brands like German Reinhöfer for 100 EUR/piece or as top product with c-cores from Lundahl for 250 EUR/piece. There is no need for exorbitant expensive Tango or Tamura iron.

Selection of nos driverstage tubes from Mullard and Rogers. Nos power tubes from Mullard, STC, GEC, Vostok,
with oktal adapters are they all pin compatible, as well have matching working point. (Does somebody remember the tube box?
Yes, the British license STC 4300B was packed identical.  ;-)

If you want to get further into audible perfection, you might profit completely from a diy project against a off the rack production from established brands,  than you should match your finalized amplifier with a so called Boucherot Element at the secondary of the output transformer to your paticular speaker/crossover (again You will not only get a safety element for the output transformer, when a speaker cable fails on power, you will get a superior matched combination. Such a matching is able to shift the sound abilities into a certain level of performance, since the impedance peaks of your speaker get flattenend. You will get rewarded with a extraodinary dynamic, open and naturally refined soundstage, without equal. Such an amplifier will be able to transcript the recorded air between instrumentation in a true natural scale, just like to perform a wide and deep open scaled dynamic soundstage, an aspect I always prefer beside tonality as my major criteria for aural excellence. Such an amplifier acts so sophistcated, that I couldn't imagine the result before I started this project, otherwise I argue with myself now why I would have done it some 20 years earlier, but I would't been able to do so back than. Such impedance matching makes as well complex loads possible, like a typical vintage 15 inch coned voice coil in the 12 ohm dc – 3mH section. You will be rewarded with a well matched partner with 6 watts output power, able to drive your vintage immobilias from Altec, Tannoy, EV or Klipsch.
By far the most of commercially available single ended amplifiers cannot outperform the classic push pull designs in this discipline of speaker control. Such always have been named to be short of power reserve to do that job well, which have given them a general poor reputation. The floods of copy and paste chinaware within the last one and half decades for peanut prices and glossy cases, have ruined the credibility of the single ended amplifier topology to a final stage. But it is more than worth to give it another try.

For some it might look chaotic, others know direct solldering to the tube socket is the best sounding variant, highly improved to any series production board or printed circiuts. Here the decisive coupling capacitor from nos Bosch production, some carbon composition resistor and Rosenthal non inductive ceramic wire wounds.

In Sound Practice Issue 14 Herb Reichert stated in an article about a completely transformer/choke coupled push-pull amplifier, the so called "Feral Eye": "This amp, ... has what I call a lubricated clipping characteristic. It has a sort of James Bond like poise ... The Feral Eye plays music very differently than most of us are likely to have heard before. It sounds more full, whole and complete than any traditional PP amp I have experienced. " Since I have finished my single ended amp I can state a similar experience here, a lubricated fluidibility, which I have never experienced before in such a scale. I am absolutely convinced about the fact that the reason for such attidude, just can be found in the improved coupling of only two tubes. Such a majestic attidude is hardly found in other amplifiers, this rare effect, it is prominently credited to transformer coupling. I can state that this particular bahavior for me justified within all my built preamplfiers, the employment of output transformers and plate chokes as to be higly superior for that reason to any other solution. It is a interesting fact, that now here the same advantages popped up with a precisely optimized conventional topology. 

Low impedance filter section with huge paper capacitors and and smoothing choke – a must. Solid wire as well.

But I have to regret, when I started to finish my Cary wrack after years of convinced ignorance (again religion), I didn't expect anything special.  I had no need to change my always winning team for something different. Recently my mood grow to realize it, it was laying around for so long: "You have bought some output transformers some 15 years ago, now just do it. If it fails your claims, it will be sold in the bay next year.
I never anticipated such an outstanding amplifier, which has already set my long time favourites, the Leak TL12.1 into retirement, and this happened with every respect and so well deserved.
If we weren't already a dying group of white old men with strong established attitudes and a lot too much possessions, I would go as far and try to realize in a small edition a series of amps, based on this experience with Taiwanese copied WE91A chassis/housings/cases, with tetrode tubes and Lundahl iron inside. An amplifier for those who need to find the final thing for a final chillout on an island, – but this idea looks like another Christmas fairytale in the wrong religion group.

For everybody a well shaked coming year 2018 with lots of wishes becoming true

P.S.: "Tamensi movetur!", Galileo Galilei, Pisa, 22.6.1633