In the history of legendary tube constructions Amperex / Philips must be acknowledged as a forerunner in modern tube technology. Worthwhile to mention are the extraordinary frame grid Amperex 6922 (read pinched waist), the long Plates ECC83 and ECC82 as also the amazing Amperex 7316 to name just a few.
In this essay I will cover the 12AX7 and the 12AU7 Amperex Long Plates Foil D Getter tubes made in the mid of the 50ties (last century). These legendary tubes are nearly vanished from circulation – but if you have the chance to grab such a tube – DO IT!!!!! – nothing compares an Amperex 12AX7 Long Plates Bugle Boy oder the 12AU7 when it comes to render female vocals!
Why is this stuff so special??
If we measure different tubes in a given circuit with white noise and analyse the outcome with an Audio Precision System One frequency analyser we would not believe what we will observe. The difference in rendering a somewhat flat frequency spectrum from 30 – 20Khz is nearly negligible. One might think our ears poke fun at us – because we can detect tremendous differences if we compare different tubes of one type from different manufacturers, which are all differ in their construction not to forget the different materials which were chosen.
If I do a test with some people who are not into High End audio – and let them hear one specific piece of music with 3 different ECC83 /12AX7 in the gain stage of the power amplifier – all will agree on a different sound and nearly all of those probands will describe those differences in a comparable way. So what is going on….?
Our test method fails at this point – the sound difference of those 3 tubes is not so much in their frequency spectrum while giving them a static signal (white noise) – what changes everything is the dynamic behaviour of them! If we measure the reaction of the same three tubes to a short burst using different frequencies – the picture is completely different. Lets say we compare a Telefunken ECC83 Smooth Plates, a Mullard MC1 Long Plates and an Amperex Bugle Boy 12AX7 Long Plates (Foil D Getter) – we are in for a big surprise….
The Telefunken is able to render nearly the whole spectrum of short bursts without any compression – there is a slight amount of it detectable in the lowest octave as also some overshooting behaviour in the higher presence (around 4 Khz).
With the Mullard MC1 we have a complete different specimen, the Mullard compresses a broad section of the presence band beginning at 1,8Khz and reaching 6Khz. The character of the compression is comparable with tape saturation of our 1/4″ master tape recorder working with 19cm/sec. It is a compression character you cannot mimic with any computer plugin nor with anything else other than using a Mullard MC1. The bass as also the deepest frequencies near 20hz are rendered with a great openess and a very lively dynamic. In the deep midrange the Mullard overshoots slightly which gives this tube its sensational warm und 3D character in this frequency spectrum. The Mullard is about the deep midrange, about the base of the music, the fundament!
The Amperex 12AX7 Bugle Boy is the contrary of the Mullard MC1… The Amperex compresses the lower midrange, where the Mullard overshoots – and in exactly that frequency segment were the Mullard does its tape compression miracle the Amperex is completely open und highly dynamic – no other 12AX7 comes close in rendering the presence and upper presence in such a lively way as the Amperex 12AX7 Bugle Boy (the 12AU7 does this in an equal fashion).
Micro dynamic shades are a kind of resolution we often forget but we must accept that this kind of resolution is very important – it makes us believe that the sound in front of us is real – micro dynamic resolution is the miracle behind a 3D rendering and makes us listening to music in an attentive way. The third dimension in a mix or mastering has nearly nothing to do with high frequency resolution or extension. If you want to prove that – buy some tickets to watch (and listening) an old black and white movie in a good cinema with a proper sound installation. What you will hear is a sound on film process, which has a treble roll off around 8Khz and it is mono – now listen to some of the great movies of the black and white era – and you will prove me right – you have every plane in the third dimension clearly displayed!
The Amperex 12AX7 (12AU7) Bugle Boy Long Plates can do this trick in the important Fletcher Munson frequency spectrum were our ear is very sensitive. Just plug such a tube in ONE single circuit position – lets say the one and only gain stage in your power amplifier and put on a record with a well displayed female vocal – lets listen to Ella solo with just piano…..every breath of her is right in front of you, every labial is rendered so damn real that you think she is with you in your room….The distance between the vocal and the listener is dramatically reduced – you think you can touch the sound source….a very special experience! I call that acoustic sex….
Now you might think – hey give me more of that – and you use such Amperex tubes throughout any 12AX7 or 12AU7 position – and……it sounds like shit! Tubes like the famous Mullard MC1 or the Bugle Boy 12AX7 Long Plates are so special, that we can use them just in a small dose – we must use them as a top chef in its kitchen – a good meal is made of different spices mixed in a very distinguished way – and not in a fashion of – one thing fits it all (hello – do you have ketchup…..???)
The Amperex Bugle Boy 12AU7 Long Plates
With this tube we have one of the best options in the critical 12AU7 / ECC82 family….be it a phase inverter or a second gain stage – this tube will do a fantastic job. Especially in phase inverter positions this tube sounds amazing….and I know that you think – “it is just the inverter position” – the importance of this section implied in a push pull circuit is not widely understood! If your inverter stage is combined with the driver section for your power tubes, the Amperex 12AU7 is also a very good option which cannot be said of all European super – tubes….With a gain stage things depend on what quality you bought. As these tubes are nearly vanished from any selling platforms as also seldom offered by professional tube dealers, we often get used stuff – they are called “pulls”. Those pulls may be “lived” in an electronic gauge or some gear seldom used – but today heavily used tubes are often sold as nearly NOS… So we will have the same situation as with the Amperex 12AX7 Long Plates – we have to live with what we get….and normally those tubes are not anymore phono grade quality. That does not say anything about their electrical parameters, which might be very, very good….what I am talking about is microphony – and as both tubes feature long plates – there is a great chance that you will detect some microphony in a phono circuit or a line gain stage. It is strange, because a Mullard MC1 or the famous CV 491 (ECC82) are not prone of electromechanical noise – the Amperex is critical in this aspect. So in most cases we can use the 12AU7 Long Plates in a phase inverter stage – if we are lucky and the tube shows no microphony – do whatever you like to do – but keep in mind – the secret of tube rolling is in a balanced mix….
If we think it would be a good idea to pair an Amperex Long Plates with some of the legendary Mullard Long plates – it is not! Amperex long Plates needs something neutral sounding aside of them – so – you might guess what follows now….pair them with some nice Telefunken ECC83 – and you achieved a miracle!
The Amperex Bugle Boy 12AX7 Long Plates
The 12AX7 is as legendary as its stablemate the 12AU7 – it is an excellent option in an amplifier gain stage or line stage. As the microphony problems are much greater in the 12AX7 family of the Amperex long plates (because of much, much higher gain) the use in a phono stage would mean brad new real NOS stuff….if you find them – you are a lucky guy. However – in a phono stage a tube has a lot more to deliver, than just gain. If you put such an Amperex in your phono stage there might be some tube rush and the presence of clicks and ticks will drive you crazy. The Bugle Boy Long Plates are not as quiet as a Telefunken ECC83 nor are they so damn good in sending all the little nasties away from our perception. In other stages these tubes make much more sense – and will deliver an unforgettable sound. You get this sexy vocal performance and a sensational string tone which has a slight preference to the bow as to the body of a string tone. But its not said that the Amperex 12AX7 will have a weak bass performance – far from that. In fact this tube can deliver a very tight, deep and impactful bass with an amazing dynamic. The deep frequencies are rendered very fast and accurate while the midrange is fleshed out and very natural but on the more neutral (not tubey) side of warm. Because of the phenomenal microdynamic performance in the upper mid section as also the presence the Amperex sounds very meaty in this frequency range. These rich tonal upper midtone colours slightly prohibit a sort of airiness. The tube sounds not rolled off – but it is not the last word in airy sparkling treble performance – these frequencies are there – but a good portion is masked by the frequency spectrum right below the highest treble. From the upper midrange on you will detect a phenomenal richness in texture and tonal content. Amperex Bugle Boys are intoxicating!
The printing on the tube – or how to spot an original
These Amperex feature the famous treble clef comic printed on the glass of the tube. But there is a good chance that this printing vanished over time – those calc paint is extremely fragile – and often mess the printing up while trying to liberate the tubes from their boxes. So how can we be sure, that we have an original tube in front of us….
There are some special traits we have to discuss:
If you observe the upper glas dome of the tube there have to exist 4 segments, divided by small glass ribs. The glas tube is thick and tall – if you compare it with a Telefunken you will discover how skinny the Tele is….;-))) The etched code must have the Delta / Triangle code of all Philips made tubes, and the plant code for Heerlen, because all long plates of these time were made in Holland. The inner structure features 17mm long narrow grey plates. The getter structure is very unique….it is shaped like a capital D with a big foil strip attached to it. This is the reason why tube freaks designate these tubes also as Amperex 12AX7 Long Plates Foil D Getter.
The same tubes are also in existence with a Philips logo printed on their glas – Amperex was a trademark found for the US American market by Philips – but it is just a trandemark – so there is no difference in sound nor in the built quality! Much later in the history of Amperex / Philips the latter installed production plants in the USA (Amperex New York) as also development departments, so there are pure US American Amperex tubes in existence which feature a different print and etched code. None of the famous long plates were manufactured in the USA.
As the American market was much, much larger than the European one – the chance to get these tubes with the Amperex imprint is much higher than with the Philips logo….in other words – the European market has nearly dried out! In the USA there is some stuff left – very expensive but if you ask me – it is worth the money and the patience to get those legends.