Monday, 13 March 2017

Revisiting my Favourite Sounds

Hello everybody,

reading on here. Today I want to describe a revisit to my favorite audio set. In a former series of articles I did describe Mikes setup as a typical LineMagentic/Western Electric installation with 22a-horn, 555-telephone, 597 hf-unit in combination with a h-dipole enclosure (with compliments to the original WE TA-7331) incorporating Klangfilm KL-405 low frequency-speakers (Incredible close to Music I – The System Matching).

This particular shown audio installation has set the pace for years in several audible terms for me. One rarely found effect was the general ability to play any sort of program material without any inherent preference. Typically the mass of better audio sets shows mostly such preferences, i.e. like intimate small scaled classical or jazz music, or large scaled orchestra and opera music or as third option, a clear distinction into electrical amplified rock or pop music. Mikes set was frankly said immune to any sort of compensation its inherent sound destinction. It always made me speechless when he played large orchestral music and switched to a pop band like Yellow, both played with almost 100db loudness without any sort of compression or other typical widely known errors...
For years Mike tried to improve a little here and there, some minimal changes did happen, but in general he seemed to follow a deep insight, made with this combination of components after 30 years of testing and changing. This particular combination marks a solely found apex, where everything seem to match perfect in balance and maximizes in colaboration to each other in a certain degree of quality. I always reminded him saying:"Never change a winning team"! To often we all had bitterly learned the lesson, when in order to improve the things, we change only one component and had lost it all – audio mikado!
I did know since two years that he was interested to test the original design of the low frequency dipole from Western Electric made in the early 1930ties with TA-7331. He always said: "I want to know how it really does sound". The attentive reader might know that in the early 1930 years in cinemas the sound was more or less telephone quality, maybe a good 200 to 5000 hz aka voice standard, far from todays audio quality, where everybody demands a minimum utopia of 20 to 20.000 hz as a result of 60 years of commercial advertizing promize.
Mikes lf-derivate dipole is a good portion smaller than its role model, made to match the sizes and preferences of the 22a-horn asthetically and made from different woods and is with best arguments a good lot less stiffer realized. The original WE-drawings are available and give perfect insight into construction, material, sizes and dimensions of the vintage enclosure. So Mike tried to copy a perfect close sample of this product. Northem hemisphere coniferous woods are today in Europe not so easy to find, but he did. He tried to copy the original design as close as possible and with some help of his friend Norbert G├╝tte he matched with unbelievable acurateness the historic role model into a today made reality.

inside different cut out adapter boards can be mounted 

Both dipoles side by side, from left the derivate incorporating two Klangfilm KL-405 drivers, next the exact copy of the WE 7331 with cutout for 18'' drivers and adapter board mounted to hold a 15'' driver. The WE design is a good 20 cm deeper and almost all material strengths of wood are almost doubled.

With his long term established installation he did incorporate a pair of 14''-drivers in dipole constellation in order to find enough low frequency energy for his set, till he uses just one simple 300B-SE-amplifier to drive the whole installtion in a passive way per channel. After testing several other 15'' driver options from Altec and Isophon in the past he did finalize with two KL-405 some years ago.
His beloved one and only power amplifier Shindo SE-300b mono amplifier drives his three way installation alone. Other fellow warriors incorporate active tube or other amps dviding for the higher frequencies in order to find enough control for the low freqency part. The Shindo amp is a true WE91A derivate, so it does convince with phantastic medium frequency tone realism and a rare fluedity as a result of a quite small Triad output transformer. The other side of this medal is a less prominent bass response, not exceptional loud nor far deep, comparing these rarities to other 300B-amps. In order to compensate this effect Mike did use the two Klangfilm 8 ohms units in parallel to find the right energy level as low frequency support without compromizing the higher frequencies using autoformers. This combination gave him unparalleled service for years.

With the new, stiffer and bigger TA-7331A dipole enclosure Mike is well prepared for examination of different driver options with matching adapter boards. Since years he has held a pair of LineMagnetic BA-15 field coil 15'' drivers in storage, which now get another chance to come into service. Independend from this pair he tried first to match only one of the 14'' Klangfilm KL-405 with than 8 ohm impedance, mounted to a adapter board into the new enclosure. A vintage Jensen or a replica 18'' fc-driver with lightweight cone and 16 ohm impedance might be actualy still on his wish list. The search for other drivers is hardly limited to paper rolled surrounds and extremely thin paper cones with ultimate cone mass of 120 grams for the 18'' versions and of course even less for the smaller variants. Such determination is result of long term evaluation with low powered single ended tube amplifier devices .A well known classic in the 15'' range is the TA-4151A or its bigger 18'' TA-4181A LineMagnetic brother will be classic aproved partners of this type of enclosure.

The evaluation 

First of all it was very interesting to listen for me to only one of his classic Klangfilm drivers in the new enclosure comparing it to the older smaller enclosure with two of them. The first impression is  well known, one driver delivers generally a thinner low frequency response than two. The doubling of the cone surface adds the physical fact of doubling with three decibel the bass energy.
But not only, one driver in the new the structure sounds a good bit better defined, foremostly in the upper registers of its frequency cut. Here we are talking about a 6 dB cut off at around 300 hz. This effect is very little, but seems to support the general transparency of the whole system up to middle frequencies.
Comparing it directly to still existing other enclosure beneath, confirms the listened new result. The double driver cabinet gives more low frequency energy, but it is less colourfull and less transparent portrayed, and  sounds a bit overtoned. At this early beginning of our audition we weren't save about the reason. Is it the size of the new enclosure with its lower possible physical response, or is it's rigidness, which gives a more uncolored deeper response? Or might it even be the higher impedancy of 8 ohms, which betters the power amplifiers ability to control the chassis? The extremely low impedancy of 4 ohms is not a ideal load for the Shindos, we have seen several other amps here with a complete break in!

The mounting of the bigger LineMagnetic 15'' driver might give answers to such open questions. First of all we talk here about a field coil driver with coated paper cone, paper surrounded, but not as lightweight as the vintage German Klangfilm cone. Another aspect is the higher impedancy of 16 ohms. From all my experiences in history it was absolutely clear that a 15 ohm speaker is always a better load to any tube amplified transformer coupled device, even when there are different secondary options at the output transformers for lower loads. A slightly bigger cone surface brings in another extra for deeper frequency response.

The LineMagnetic BA-15 with its dedicated adapter board inside the TA7331

The prepared adapter board was quite fast mounted to the enclosure, cabling to match the tungar power supply were as well ready to go. The built in passive crossover with Tango stepped intuctor coil made the quick change possible, a perfectly matching value was just a new contact of its coil.
With the first tone the sound changed dramatically. We had suddenly the feeling not any longer to listen to the same audio set, we did do for so long. Something completely new happened and shifted the overall soundstage to a former unknown domain. The sound got dramatically more dynamic with a real load of better resolution and scale. The low frequency response got extremely better articulated, still a bit withdrawn in terms of energy, but exceptionally better defined. It sounded 100% better resoluted even in the middle frequencies. Here the 22A-horn was a lot better intercepted, its enormious qualities in resolution and dispersion of the micro dynamic detail seemed to be extremely improved by now. Coming from the single Klangfilm driver, it sounded double dynamic and unbelievable better defined in the most frequencies of the complete soundstage.

What made this exceptional step forward possible? Again, do we talk about size or rigidness of the enclosure? Do we talk about a better energy transport inside the enclosure structure? Or is this step mainly build on better matching impedancies of the chassis to the power amplifier? Actualy it looks of course that it is a product of all attitudes together, but I am quite safe about the fact, that it is not the deeper and bigger size of the enclosure. It seems to be mainly solved by the rigidness in combination to the improved impedancy of the chassis as driveable load. The tungar power supply and the field coil magnetic unit might be as well in count for such a difference, but this question needs further investigation. Another options of 16 ohm drivers might be be tested soon to get safe insight. As well 18'' chassis will be in evaluation soon.
After this experience we switched the set back to its long term standard low frequency support, the doubled KL-405 in its smaller enclosure. The first impression was, there must have gone something faulty, it cannot be! It is sounding completely failed, indifferent detailed with too much upper low frequency energy, which is overlaying the horn and influencing its abilty to express and resolve in finest micro detailed structures. It is unbelievable that this sound was the highly aproved state of art for some years!
Yes, it sounds unbelievable stages better defined and with extremely better resolution over the complete tonal scale. Its dynamic articulated attitudes seem to be doubled, the projected scale of information has got widen to an extreme. Everything is there a whole lot more...
Can this be? What is the secret to double your income without more work to do? Were do you get the double output of something without changing the input? Might it be a classic case of illusion?

Yes and no. We are still considering all aspects. A rigid enclosure helps to perform higher energy levels with less contributing side effects. Different than ordinary other enclosures, which need to handle middle or even high frequency drivers, the low frequency dipole works very different in terms of resonance distribution. Here the rigidness does not influence negatively the response of the higher registers, instead the rigid construction enables a deeper response of lowest tonality without resonant effects. The weak smaller enclosure brings in a lot of unwanted resonances influencing the exceptional abilites of the 22A through thinner boards and less stiff bracing. Supported by the better handling ability of the power amplifier of a higher chassis impedancy and as result a much improved sound structure, the stiffness adds up to a extremely better articulated refined sound in general. 
Mike is actually very impressed by such a differend result and will continue the evaluation process with other low frequency loudspeakers to find out more about such improvements.

But no sunshine without shadows. My personal rating is a bit more complicated. First it needs to be examined how a better postitioning of the units, which is actually not ideal to the listening place, will influence the result? Actually the sound stage is very complex and inhomogenous. Its difficult to find a smooth projected imaging of the music with naturally scaled instruments. Listening for more than two hours to music showes me several other inconsistencies. The former unbelievable attitude to play any sort ot music programe has gone. Instead the system shows up with very clear preferences to some small scale arranged music. Larger scaled classical orchestral music is played (let me say it carefull) with several problems. The sound structure is exquisitly detailed but at the same time shows tendencies to dry out and starts to get a bit cheeky. The low frequency response is extremely articulated but does not really seemless intergrate into the huge soundstage. It might be a problem coming from its physical ordered placing side by side of the other components. In former times the units were placed in optimal triangled composition in Mikes listening room, now they are far more positioned in distance to each other. The soundstage was before completely three dimensional holographic in a small centered listening position. It took not even minutes to forget about its coming into being in terms of technical realisation. I was able to forget completely its artificial sensation and accept it like a naturally released sound from an instrument. Actually in the suboptimal positioning of the new enclosures, the sound is some sort of disintegrated and dismantlet. Horn, tweeter and dipole seem to come from different origins, a problem very common with such horn installations, but again before completely unknown here, now very prominent.
To me such little defects are more or less inacceptable, till I am used to my Tannoy Dual Contentric units which are almost point sources and are able to convince with a lot bettered homogenous projection and a almost holographic sound stage.  If you get used to such a speaker you are extremely sensitive for any sorts of phasings and time incorrections. Mikes new set has lost some of his former major qualities of a holographic soundstage in exchange with much improved dynamics and far better resoluted micro detail. I hope he will readdress these lost attitudes to his new system some day again.

But as well our audition has shown several unknown new facts, which need further investigation.
My personal conclusion would be a stiffer baffle board for his smaller old dipole enclosure and I would search for some fast and expressive, hard edged light weight paper coned 15'' chassis with 16 ohm impedance; if it needs a permanent magnet or a field coil is a still open question? As well the 18'' driver needs to be evaluated some time, if it can sing, we never might know – the answer is going to be a bit expensive. The main question is for me, is it worth to give all the positive cooperative results away for just a little better resolution and dynamics? But it is like always, once heard, it is difficult to struggle back.
With such dipole enclosures the bass chassis can give very different sound directions into the whole system. It is a bit like a typical wine tasting process, there will be some extremely different tasting candidates out there. Each of them will shift the general sound stage to other illusions and its just like the wine, you need to find your personal favorite...

Some people prefer beer against some wine, the active driven solution is just a whole own story to find ways into heaven. i am sure it will take years to find a way...

Read on soon,

Saturday, 25 February 2017

Lessons of History – Japanese Achievements

Hello to everybody reading on,

today I would like to respond to a rare experience with seldom seen tube audio equipment from a japanese manufacturer. Here in Europe it is normally impossible to evaluate different handmade japanese audio products, which were made over there within the last 40 years for a highly exclusive market of experts. Ken Shindo's line of products is quite well known in Germany (i.e Central Europe) since the care of Auditorium 23/Keith Aschenbrenner and his introduction about more than 25 years ago has Shindo established as a top line of tube amplifiers. Major other products are hardly seen outside Asia, a known problem derivating from culturel differences in language and scripture. So even today, 20 years of information blow out through the internet, our knowledge about different audio brands in Japan has been improved only a little. But to own personal experiences with such handmade products is still almost impossible.
I got the rare chance to evaluate a complete set of products from the Japanese manufacturer P&C, i.e. a so called pair of PP 50 power amps and their dedicated preamp together with P&C-version of the legendary WE 618B step up transformer.

P&C 50 PP mono amplifiers based on WE 86 B amps, here with EML 300B mesh anode tubes and
a pair of type 27 triodes as two step amplifier stage (1. shielded) interstage transformer coupled in
combination with a pair 5U4 rectifiers forming a bridge in gray hammerite paint.

P&C amp is a audio business, which was found in Tokyo 30 years ago, in the days when the reinvention of historical tube audio culture was main topic there. Toshiaki Kurashima started a main business with the rewinding of original Western Electric cores of the 1930ties from junk telephone equipment. Made with their original winding instructions for audio use in order to find sources for modern build amplifiers on the tradition and superiority of famous vintage Western Electric designs. Through the years he managed to replikate all major magnetic coil components like output-, input-, stepup- and power-transformers in order to rebuilt a wide range of vintage WE-amplifier designs. On top he completes this range of original designs with modernized and and variied own types of amps with similiar topologies and a wide varity vintage tubes. Some people might remember my article about the Hong Kong based Mr. Wu, who is doing a very similar business with some main designs from Western Electric over there. We do learn that in Eastern Asia some people highly prefer old vintage iron cores about modern recipies of manufacture, like glassmetal or other armorph core materials. The published arguments are always the superior naturallity and coherence as quality argument, which never got matched by more superficial contemporary materials.
My first impression of the build mechanical quality of these amps is just amazing. Their physical size, their weight and their appearance is a top notch product – Bentley quality in tube amplifier terms. All switches and contacts are massive and solid made, plated to highest standards. All knobs, stepped switches and attenuattors are highest quality Seiden switches. The incorporated parts like resistors and capacitors is the best possible vintage range, like 2-3 watts Allen Bradley carbon comb resistors, together with vintage Sprague PIO caps and Mallory sealed electrolytics. All these parts are hard to find in NOS qualities today. The sheet metal used for the enclosures is more than solid, 2,5 mm carbon sheet steel ist used throughout. One of the mono amps weights a good 25 kg at a size of 50x30x25cm. Two of them need real space, the preamp is a monster with another 50x15cm front plate and good 40 cm enclosure depths. Before you start to listen you may need to find longer interconnects to get proper connections in between.

P&C preamp

Some might argument the preamp is ugly, but some can as well say it is shining in a foremost technical intended appearence and renounces any sort of decorativeness, which is common with other more commercial distributed audio equipment, like golden knobs or shiny face plates. Inside the P&C's a almost professional finalisation of hardware is shown, only known from vintage studio amps. Such a modular design offers a wide option of combinations, here you see three functions: first a power supply module with tube rectifier and C-R-C-filtering, second line amplifier module with two WE 396 tubes, transformer coupled with vintage Triad output transformers to 600 Z output impedance.
The phono stage is a two step R-C-Riaa design module, based on triode connected WE 403A tubes. The output stage here is as well transformer coupled to the line stage. Such a topology with output transformers coupling is generally rarely realized topology for audio components and foremostly again found in professional studio equipment of the tube age. Today seen as another rare delicassy, this preamp features sound shaping components, very different realized comparing classic variable R-C-filter designs known from consumer audio components, which always degrade the sound quality. Here the potentiometer acts as a variable resistor in the feedback loop, so the sound can be opened up in scale, resolution and presence by adjusting the pot. Additionally it features a certain potentiometer to adjust a low frequency boost. Both options feature a rare luxury to adjust the general sound shape to individual preferences or to match room dispositions.

Modular design, all stages transformer coupled with vintage Triad OPTs, all tubes vintae WE types

This preamp sounds very lush, easy and with a bit of tenderness, but without compromizing any detailed information nor forgetting to keep the timing aspects in a naturally embedded flow. The general sound is extremely gentle and noble, maybe a typical japanese attitude and so it makes the listening to any sort of music program material to a luxury event of restrained purity, similar to the taste of freshest cut yellowfin tuna fish for the traditional sushi event. Unfortunatly this preamp is not any longer made, since its vintage components are out of stock. But P&C offers other unique models, one is equipped with in Japan famous LCR-RIAA module, of course based on a WE-design featuring vintage WE-iron for the important inductor coils!

Coming to the pair of 300b PP mono blocks. My first impression of their sound was quite unexcepted. I did expect a warm and detailed typical 300b-tube-sound. In push-pull configuration these little monsters should power a good 15 watts output and such energy should be able to drive any vintage efficient loudspeaker, so my 15 ohm Tannoys should find a perfect matching partner. These amps are able to drive even less sensitve speakers than mine pefectly, they show up with a very distinct rounded soundstage with a absolute main intention into the warmer side of the tonal spectrum. This particular topology seem to be aimed to optimize drivability. But this impression has to be seen together with the used type of 300B tubes, I did listen to Emmission Labs 300B Mesh's. Other tubes might change the sound texture of these amps totally, since the design is completely build on transformer coupling, one option to keep capacitor degrading influences as low as possible. Otherwise these amps might be adjusted to a the range of vintage Altec products, to keep their sometimes over prominent performance in presence back into control. From P&C's web side it is known that vintage Altec speakers are used in their workshop for all sorts of evaluation processes. Neverless these amps perform well with a clear overall refinement in their music representation, which is hardly found in more typical to western worl taste tuned american commercial tube equipment. These amps feature all the goodies from the historical Western Electric range, here the transformer range of the WE86B push pull version of their 300B amps. Reedited output- , interstage- , input- and power- transformer, together with choke, rewound on original vintage Western Electric cores, make this amps a rare and unique option in the global range of 300b-tube amplifiers. These powerfull amps are a perfect solution for those who are looking for more control than the typical WE 91A single ended amps are able to deliver and do prefer some more lower and upper bass energy than its historic role model. P&C does recommend modern made Emission Lab tubes for those who don't be able to run the value of a medium sized car for daily service in audio with vintage Western Electric tubes. The EML 300b's Mesh are some of the best modern replacements for the crazy priced vintage originals, I personally like them better than any Asian make.

As a exceptional delicassy some of the vintage transformers from Western Electric are sold for sky rocketing prices.  So the input devices WE618A/B/C/Ds are the most expensive input transformer range used for moving coil step upt. The WE618B with a ratio of 1:20 is a ideal step up transformer for the popular Ortofon SPU's and similar cartridges. Originals are sold for 5000 to 10000 $ per piece and chanel, due to their rarity with no limmits in comming future. So it did make sense even some decades ago to find other ways to get hold of a pair of this particular design. P&C did find out about the used core materials, original winding instructions and evaluated expertise to find the right cores in other vintage components. Mainly old telephone equipment from Bell Laboraties did use the same core packets with other winding schemes. For example the WE 111 splitting line transformer incorporated the same iron core like the WE618. These cores rewound to the exact winding scheme of the vintage WE618-types gives ways for modern samples of the hard to find originals. Now I had a first chance to listen to one of these replicas made from P&C in my own chain.

P&C version of the legendary input transformer, used as step up transformer for moving coil cartridges

The replica sounds amazing in several terms. With a exceptional ease and flow this step up transformer represents the tonal attitudes and a wide spectrum of the Ortofon SPU to the ear. A certain stage of refinement in flow and delicate resolution, most other step up transformers hardly can match, make forgetting the process of tracking a vinyl groove. A naturalness of refinement make it exceptional easy to follow the internal energy of musical intention. At the freqency ends it is loosing little bits of energy comparing amorph cored competitors, but its exceptional homogenous presentation of the main frequencies is its beating counter argument. It declares the most other products to a second rated choice and it is operating absolutely hum free. Only a few rare step up transformers will be able to keep competition with this little wonder. Based in MU-metal cases and equipped with sturdy RCA-contacts, this device is a real option for those using SPUs, all other moving coils cards may need to look for the brother 618A with differenet step up ratio. With around 1.5 K$ cost in Japan both transformers are still in the payable range ...

The P&C components which I could inspect and listen to, are so well made that they seem to offer a lifetime value of perfect service with exceptional musicality. Their sturdyness and physical presence is without equal, you just need some tubes fom decade to decade. Make sure to have enough in stock.

Read on soon,

Tuesday, 10 January 2017

Audible Drugs – Valvozepam or Tubalkaloides for the Addict

Hello to everybody in new 2017!

From time to time I will try to publish this year some new articles within my blog when there are some interesting topics about vintage audio are comming up. I hope to publish another "deep interest"-interview with Michael Fountain, son of Guy R. Fountain, founder of the Tannoy Company in the early 1930ties of the last century. I am looking forward to publish this in spring time with some unknown insights into the design and development of the famous Tannoy Dual Concentric Loudspeakers.

Typical GEC KT66 from late 1960ties production

For today I am resuming my expedition into beam- and power- (pentode/tetrode-)tubes of the 6L6 family in order to find valuable replacements for classic KT66 tubes, the by far the best sounding power output tube of this type, unsurpassed from any modern replacement. All members of this family show up with amost identical electrical operating points and might differ sometimes in heater consumtion and all around construction details, but are more or less compatible, but may need adaption of their socket. The british GEC KT66 is the crowning archivement of the golden age of tube amplification, so it is today the most sought after power output tube for the standard push pull amplifier types. These "Kinkless Beam Tetrodes" have been used with loads of classical tube amps, independant if we are talking about audio-, pa- or guitaramps. Within 20 years world wide sales through the internet and ebay the actual price range for original GEC NOS tubes has been sky rocketed through the roof and in particular guitar players seem to pay any price to make their amps sing. But as well in the audio world the original tubes are famous for their incredible sound opportunities, never matched by any modern replacement in audible terms. This might explain that a quad of four NOS GEC tubes is priced beyond the 1000 $ line, no question that it will explode into the 2000 or 3000 $ range within the next years, when they get even more scarce. This market mechanism can be observed for decades when looking to the price development of the legendary original Western Electric 300B tubes from all different production times between 1930 and 1988. This might give an idea for the coming future of vintage audio tubes. No question, vacuum tube business is getting comparable with drug dealing, in terms of profit and as well in dealer attitudes, but it is still legal?! Valvozepam, Tubalcaloide, who has the one and only pulp?

How can it be, that since 30 years of business in reproduction and replication of tubes made in China, Russia and from former East European Countries, which are sold for a fraction of the price of the original vintage tubes, – fabricted with all modern knowledge, sometimes at the original production machines, – not even one tube did match the standard industrial production quality of the business back in the 1950ties? And to be honest, not one of these tubes matches the magic, refinement, spacousness and natural dynamic atttudes of the vintage originals. You can get two new quartets of chinese replica KT66's (looking totally identical in physical terms), for the price of one single used original tube? What is the true hidden secret of the industrial age of the 1940ties technology, if it can not be transfered into todays production process in China or somewere else?
People pay tremendous amounts to get the original GEC tubes after they have evaluated modern substitudes, because not one of the modern reissues matches 50% of the tone coming with the "drug-like" originals.

Today I want to publish some of my experience with other vintage tubes, which show up with a rare quality range and ability to replace the phantastic soundung GEC KT66 into a seemless matching sound texture with only very little restriktions. The only difference is in common the mechanical matching of the tube socket. For this reason there is already a commercial solution, if you want to use a "tube-socket-adapter" to match your original octal socket, these are available for amost any tube and their dedicated socket from a dealer in Taiwan selling these on Ebay for about 20 bucks per piece.

GEC KT8c from 1940ties production with blacked anode plates and ceramic B5 socket

The first tube which I want to present today as a "better than original" replacement for the GEC KT66, the second world war production GEC KT8 or KT8c. The "C" marks the ceramic socket, where the standart KT8 tube shows up the a classic bakelite socket. The tube is equipped with a widely used 5-pin Euro socket or more internationally spoken, a B-5 socket. Additionally this tube is equipped with a anode cap on top of the shoulder shaped glass envelope. This tube is extremely similar in construction and internal design to be found in the first "coke-bottled-VT75 tube", the forerunner of the standard KT66/CV1075 as known today. These KT8 tubes have  been made as british answer to the US-american 807 beam tetrode for the use in plate modulated RF-amplifiers. But the KT8 failed the aimed quality in particular in the 125MHz operation target comparing the american 807, which was already a standard in this type of application in these days. This fault is our luck today, the KT8's are still available in a small amounts as NOS tubes from several british tube stockists (Langrex, Colomor, Billington, etc.) for about 60 EUR a piece. Their hf-fault does not matter in the audio range and so for that amount you will get a wonderfully made vintage tube, which ressembles the MOV/GEC KT66 originals in more than perfect matters for audio use. These tubes are all little gems soundwise within standard 6L6-applications, like in push-pull audio or guitar amplifiers  and match the lengendary first "coke-bottled- KT66 made by Mullard-Osram-Valve-Company, indicated by the legendary oval etching at the glass. These first KT66 tubes are exorbitant rare and they are together with the Western Electric 350B's the most sought after type of all 6L6's, reflected in their actual prices at 800-1000 $US per tube.

One GEC KT8 and one KT8'c with Taiwan socket adapters to match the classic octal socket

Another very good option to replace the KT66's are the exceptional cheap NOS 807 tubes equipped with a another tube socket, made by a wide variation of different manufacturers. These tubes do sound all around very close to the before described KT8 tubes, but are cheap as peanuts and they are available in big amounts. Out there are as well NOS Russian types from the 1950ties, but I don't have any personal experience with these. The 807's are as well beam tetrodes like the KT8's and they do sound phantastic as well. A little bit different in the general sound attitude, but as well very refined, detailed and show up with exceptional natural dynamics, light years better than any modern replacement. The experimental intended user might be interested into a british loctal 5B/254M tube type made by the famous STC (Standard Telephone Company). This small glass enveloped tube is a direct replacement for the 807 tubes with a loctal socket and they are cheap. But there are no ready made adapters available from the Taiwanese supply on Ebay, here the adapters have to be self made.

Two different NOS 807 tubes with octal adapter sockets

STC 5B254M tube with loctal socket, here the interested needs to make own adapters
in order to match the 807-replacment to any other socket type.

All these vintage tubes show up properties only vintage tubes come along with: finest micro detailed resolution, open refinement and fast translucent sound structures with exceptional natural dynamic attitudes, together with a today unknown sweetness in tonality. These 10 to 20$-tubes make any modern 6L6-replica sound like a audio diet or degrade them to placebos for the addict.
If you are planning to substitude in your vintage gear your 6L6-type tubes with vintage equivalents like the here shown tubes, you must first check your actual limits of heater currents in your amp. The filament current might differ within different tube types and make sure that your amp will not be set to swallow or even more will get damaged by increased heater currents!

I might continue the series about tube rolling with some Bendix 6889 tubes or some 5881 tube types of different origin. Anyway they will be at the payable side of life and do compliment the here shown tube line very well.

Read on soon,