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.
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| 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.
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| 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 $US per tube.
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| One GEC KT8 and one KT8'c with Taiwan socket adapters to match the classic octal socket |
Another very good option to replace the KT66's are the exceptional cheap NOS 807 tubes equipped with a another tube socket, made by a wide variation of different manufacturers. These tubes do sound all around very close to the before described KT8 tubes, but are cheap as peanuts and they are available in big amounts. Out there are as well NOS Russian types from the 1950ties, but I don't have any personal experience with these. The 807's are as well beam tetrodes like the KT8's and they do sound phantastic as well. A little bit different in the general sound attitude, but as well very refined, detailed and show up with exceptional natural dynamics, light years better than any modern replacement. The experimental intended user might be interested into a british loctal 5B/254M tube type made by the famous STC (Standard Telephone Company). This small glass enveloped tube is a direct replacement for the 807 tubes with a loctal socket and they are cheap. But there are no ready made adapters available from the Taiwanese supply on Ebay, here the adapters have to be self made.
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| Two different NOS 807 tubes with octal adapter sockets |
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| STC 5B254M tube with loctal socket, here the interested needs to make own adapters in order to match the 807-replacment to any other socket type. |
All these vintage tubes show up properties only vintage tubes come along with: finest micro detailed resolution, open refinement and fast translucent sound structures with exceptional natural dynamic attitudes, together with a today unknown sweetness in tonality. These 10 to 20$-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,
Volker
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