Bottlehead Crack

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by OJneg, Oct 3, 2015.

  1. Jeb

    Jeb Friend

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    I've been exploring different output tubes for the Crack over the last few months and wanted to share my experiences and the notes I made at the time. To be honest It's not something I would repeat if I had my time and money again. It's not that the differences aren't noticeable or even worthwhile - but more that while it started as an enjoyable process of discovery, eventually chasing different tubes & focusing on their sound became pretty damn distracting from just relaxing and enjoying the amp. Apart from a couple of fairly nasty sounding tubes I really don't think it matters too much which tube you use. But there are notable differences in the sound described below.

    My time would have been better spent just fitting the Speedball & other Mods. You live and learn.

    As with lots of tube types, re-branding is all over the place with the 6080s/6AS7 family so i've included pictures so anyone interested in trying different tubes can check the internal structure and avoid potential screw-overs from dishonest or careless sellers. There was someone recently selling Russian 6H13Cs with GEC stickers.

    Of course, always best to make your own explorations & be extra suspicious/dubious of tube "guides". They are are of limited value - especially those written by SBAF newbs like me.


    Headphones used were stock HD-650s.



    PART 1: 6080s



    Thomson CSF-6080WA

    Price: ~£8 each
    Availability: excellent


    French military tube from 60's to mid 80's. Often comes in the original ridiculously oversized boxes. Clean, Airy & delicate. Nice treble performance. Well extended with impressive decay. Sparkly. Sweet sounding but could be a little bit metallic and a little thin sounding overall & especially in the mids. Good bass definition but may be bass-light for some. Works well with HD-650s. Nice budget easily available tube. If you got an RCA 6080 or GE-6080 as the stock tube then Thomson can be a worthwhile upgrade.

    Treble: 8/10
    Mid: 6/10
    Bass 6/10

    Overall Performance: 7/10
    Value for Money: 9/10


    [​IMG]

    [​IMG]








    Sylvania 6080

    Price: ~£10-£15 each
    Availability: very good

    Also available as WA/WB/WC iterations (chronological improvements) which may sound different. Tonally very warm & soft. Liquid. Smeared & Blobby. Pretty Bleh. Lacking in dynamics, overall impact & detail is obscured. Mid-centric & slow. Poor extension at the top. Pretty nasty overall. Poor choice for HD-650s. I would skip it. Apparently later versions (with steel rather than the earlier copper grid rods) tend be noisy.

    Treble: 1/10
    Mids: 5/10
    Bass 4/10

    Overall Performance: 4/10
    Value for Money: 5/10


    [​IMG]






    Tung Sol 6080

    Price: ~£15 each
    Availability: Average

    Cool looking tube with classic looking US print. Also appears under Chatham label. Cheap but doesn't seem to be loads of them around. Damned good sounding tube! Clear and wide but with extra bite - just what the HD-650s needs. Punchy & Holographic with vocals a little more recessed but well placed for me. Well extended in treble. Dynamic. Sounds quick. Tight bass with good attack & weight. Guitars have excellent tube "twang". Sometimes could be a little bit grainy sounding. My favourite budget tube if not one of my favourites overall. Gets feet tapping like few of the others. Seems in tune with the "spirit of the Crack". Sometimes ships as the stock tube in the kit - if so, no need to go any further unless you're curious.

    Treble: 8/10
    Mid: 8/10
    Bass 8/10

    Overall Performance: 8/10
    Value for Money: 10/10

    [​IMG]

    [​IMG]



    RCA 6080

    Price: ~£10 each
    Availability: Excellent

    Again, other iterations (JAN?) might sound different. This one sounds a bit richer than Tung Sol 6080. Initially sounds just average but with closer listening seems tonally very disjointed. Poor transient response & zero bite. Some mid-range & mid-bass suck-out. lacklustre. Treble can sound flat & rolled then strangely screechy at others. Weird & boring all at once. Loads around and cheap - and for good reason. Swap for a Thomson 6080 or Tung Sol 6080 asap.

    Treble: 3/10
    Mid: 5/10
    Bass 4/10

    Overall Performance: 4/10
    Value for Money: 5/10

    [​IMG]








    Bendix 6080 Graphite Plates

    Price: ~£35 each (solid plate) £50 each (slotted plates)
    Availability: average (solid plates) / poor (slotted plates)

    Super ruggedised tube from New Jersey factory with graphite plates, thick glass and various extra supports - made for very demanding situations with need for high reliability. Thick glass - makes weird whizz-bang noises as it heats up. The only tube that needed 30 mins + to sound consistent (all others stable in 5-10) - which is a bit annoying for quick stealth sessions.

    Super clean & solid sounding. Well balanced & surprisingly smooth. A hint of lushness (more than the standard Tung-Sol 6080). Instruments sound convincing, solid & well fleshed-out. Bass is slightly boosted but still well resolved and impactful. Treble extended and clear but lacking extra sparkle. Overall perhaps lacking in agility, punch and excitement factor. Might be lacking in "magic" :( Solid performer but price-tag makes it relatively poor value especially vs the vanilla TS-6080. Perhaps use something more exciting in the input slot. Looks cool as hell in the Crack!

    Slotted/ cross shaped plates more sought after and may sound different/better.

    Treble: 7/10
    Mid: 7/10
    Bass 7/10

    Overall Performance: 7/10
    Value for Money: 5/10


    [​IMG]





    Mullard CV2984 / 6080

    Price: ~£30
    Availability: pretty good

    British tube in cigar roll. Very lush. Soft as hell. Lacking in transparency, resolution, and extension at both ends. However somehow manages not to be totally boring (unlike Sylvania 6080) with pretty special and unique liquid warmth in the mids that is strangely enjoyable and not found in any of the others. Glowing, rich & a bit other-worldly. Blended and swirled. Boomy, ill defined bass. Limited bandwith for music collection - Pathetic for electronica, worth hearing for other genres. Probably too thick and slow for HD-650s overall. Might be good for Beyerdynamics with sizzle. Will use from time to time.

    Treble: 6/10
    Mids: 8/10
    Bass 5/10

    Overall performance: 6/10
    Value for Money: 6/10


    [​IMG]






    GEC 6080

    Price: ~£40+
    Availability: not great but some available at higher prices (£65) on ebay

    The less sought after of the 2 GEC tubes but almost as rare. Can sometimes be found for good (sub £30) prices. Beware people selling GE (US) tubes as GEC (British). Excellent and classy sounding tube – controlled, clean and spacious. Fundamentally warm but much less so than the Mullard and remains very well resolved in the treble and more balanced throughout. Extra shimmer and sparkle. Accurate and delicate with possibly the most impressive imaging/separation of the lot. Precise but not lean. Vocal is natural and well placed. Bass sounds well controlled but not monstrous. Some may find it all a bit lightweight/prissy. For me - the best 6080 next to the Tung Sol 6080 which has a bit more kick but isn't as refined.

    Treble: 9/10
    Mids: 8/10
    Bass 8/10

    Overall performance: 9/10
    Value for Money: 7/10

    [​IMG]

    [​IMG]




    GE 6080

    Price: ~£8
    Availability: excellent

    Came as the stock tube in the kit and I returned to it at the end of all my rolling to see how far the Crack had come. A Good starting point and still better than RCA/Sylvania 6080. Overall sounds a little compressed, a bit dull and muted throughout the entire range when compared to the best of the others - but mostly inoffensive, nothing to worry about and will certainly not prevent the wow factor when first firing up a freshly built Crack. Impressively average in all departments. Would be cheap and easy to move to a Thomson 6080 or Tung Sol 6080 for a nice little upgrade but certainly no need to if you're not into tube rolling.

    Treble: 6/10
    Mids: 6/10
    Bass 5/10

    Overall performance: 5/10
    Value for Money: 6/10


    [​IMG]



    ......6AS7s to follow at some point
     
    Last edited: Aug 27, 2017
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  2. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Nice comparisons! I'm curious to know more about your background experience with other gear and tubes so I can get a better feel for your tastes. You know, because there's a chance I might like some specific qualities that you dislike. Just want to put your tastes in perspective so I can correlate them with mine. :)

    (I'm sure this will be easier for me once I roll more tubes in my modded Crack + SB.)
     
  3. Jeb

    Jeb Friend

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    Hi Hands! Thanks!

    I don't have tonnes of experience with other gear-

    headphones: current: HD-650 & Beyerdynamic T51p. Sold LCD-2 Fazor due to feeling HD-650 bettered it in most departments & much more comfortable, of course. I found LCD-2 very narrow, fairly clean sounding but overall somewhat muffled & boring with some occassional strange treble nastiness I didn't like. I was expecting great bass but surprisingly found it a bit limp down there too. I always wondered if I would have preferred LCD-2.2 bass but I've never heard it. HD-650 hits the spot there but is also currently sounding a bit soft and bloomy with the stock-crack.

    Amps: had Asgard 2 and WA7+WA7tp, both sold and now have just the stock-Crack, which I felt was possibly technically just behind both of them but overall more engaging & holographic. In the WA7 I think I wasn't totally wild about the slightly flat & raw 6C45 sound - if that's where it was coming from. I rolled a lot of 12AU7s in the WA7 so have lots to try in the Crack if I ever want to.

    My feeling with the (stock) Crack and HD-650 is that it benefits from a quite lively and dynamic sounding tubes so that the 650s come to life and don't accentuate any tendency for slowness, veil or bass bloom. I'm pretty damned sensitive to brightness, etch, roughness or grain so those are things I typically look out for. My feeling is that stock-crack & HD-650s can't tolerate anything too "lush" warm or rolled off and I could throw something at it that would normally be too bright for me. There was only 1 output tube I rolled that I thought may have sometimes been too hot in the treble - the Russian 6H13C.

    I still need to fit the SB. A few people said that the Crack was more "responsive" to tube-rolls pre-SB so I decided to do all my rolling first. But I have no idea if that's true. As I mentioned I certainly don't want to encourage anyone to roll tubes excessively because at the end of my rolling my main feeling was that it performs very well with many of the decent budget tubes.

    Cheers - I'll think about trying to add some more different points of reference when I write up the 6AS7 notes.
     
    Last edited: Nov 16, 2015
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  4. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    You know, I have never heard a stock Crack, so I wonder if my tube preferences would change based on that. I tend to prefer a lusher, smoother sound (though still has to be dynamic and lively), but maybe those types of tubes + stock Crack would be too much. In other words, maybe the speedball and other mods make those types of tubes mesh better?
     
  5. Jeb

    Jeb Friend

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    Hands - difficult for me to say - but I think what you said is certainly a good shout. I'll have to get the SB fitted to verify. It sounds like my preferences may be in the same ball-park as yours. There were some tubes that I felt were right on the edge of what I think is acceptable in terms of warmth/lush without giving up too much detail/dynamics - those would be the RCA 6AS7G / Tung Sol 6AS7G and perhaps the GEC 6AS7G. If the SB tightens the resolution & low-end then they will likely be perfect for my tastes. Tung-Sol 6080 steers more toward neutral and is damned good.

    Others like the Mullard 6080 / Sylvania 6080 I thought were just too gloopy and would have a long way to go- though it's possible the SB could bring them back into play. We'll see.

    6AS7s coming in a min.
     
  6. Jeb

    Jeb Friend

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    PART 2: 6AS7s


    GE 6AS7GA

    Price: ~£15
    Availability: great

    6AS7GA variant from GE, Kentucky, with dual D Getters. Not sure I understand the loyal following this tube has vs the GE6080 which is universally panned. From my listening the 6AS7GA doesn’t depart too far from the 6080 tone but offers a slightly more refined experience with a little more delicacy, air and treble extension. Wouldn’t stake my life on the differences. Mids are a little more recessed giving the illusion of a more balanced and mature sound. Bass is just as flabby. Still little improvement over the 6080’s dullness and absence of dynamics - a sidegrade if at all. Neither one thing nor the other. If it comes with the kit – great! To buy it as an upgrade? – meh.

    Treble: 6.5
    Mids: 6.5
    Bass: 5

    Overall performance: 5.5/10
    Value for Money 6/10


    [​IMG]





    Russian 6H13C / 6N13S / Svetlana “Winged C”

    Price: ~£5-10
    Availability: excellent!

    Soviet. Dirt cheap and abundant. They sell them by the box-load. Very impressive sounding for the money. Lively. Great air, clarity and resolution across the entire range. Sounds big & wide and well separated. Treble well extended and particularly crisp. Low-end is tight and fast with less bleed – One of the best here & vast improvement over something like the Mullard’s bloominess. Sounds a bit raw, grainy and shouty at times. Could be fatiguing but mostly fine for HD-650s. Edges are sharp & have a little glare. Staging is wide but not particularly deep or holographic. Mids clear but vocals do not sound as natural as I would like. Damned good for £5.

    Treble: 7
    Mids: 6
    Bass: 8

    Overall performance: 7/10
    Value for Money 10/10

    EDIT: extra pics added - Take note of the construction – common to see re-branding of these Russian tubes and some being passed off as more expensive Euro/US 6AS7s.

    [​IMG]

    [​IMG]





    RCA JAN 6AS7G

    Price: variable - ~£20 each
    Availability: very good

    1950s RCA with black plates. Commonly rebranded as Sylvania, GE & Raytheon. Take note of the large “flaps” or protectors above and below the plates – a tell-tale sign of RCA.

    Warmer & more relaxed than the Svetlana – and now that seems like a good thing. Much more cohesive than the oddball RCA 6080 sound. Rich and full bodied mid-range with respectable detail throughout (but lacking vs GEC 6080). Treble is not as crisp as the Svetlana but is probably more natural with realistic decay. Bass a bit feeble in attack but decent quantity. Mid-range bleed. Warm but more dynamic than the Mullard. Vocals very pleasing indeed. Seems quite in tune with 650s signature. A nice balance if you like things on the lusher side but don’t want total gloop. Great all-rounder and probably my go-to “warm” tube.

    Treble: 6.5
    Mids: 8
    Bass: 6

    Overall performance: 7/10
    Value for Money 7/10

    EDIT: - note again the construction of this tube - this is a very common tube and it's very common to see RCA 6AS7Gs being sold as other, sometimes more expensive tubes.

    [​IMG]

    [​IMG]





    Tung-Sol 5998

    Price: £50-£80 each
    Availability: average to poor

    One of the most revered in the Crack. “Domino” plates. Sometimes rebranded as IBM or Cetron. Construction differs over the years e.g. in getter location and shape. Some tubes labeled 2399 may also be exactly the same (no complete consensus on this). Not to be confused with the 5998A. Crazy expensive Western Electric 421A may or may not be a “premium” version of the 5998. (probably isn't :-/ )

    Initially underwhelmed but latterly appreciated its charms. Spacious and transparent sounding. Great punch, dynamics and confidence. Less warm/euphonic & midcentric than RCA 6AS7. One of the least mid-centric. Just a well balanced & wide sound. Instruments and vocals have impressive body without being artificially thick or overly warm. Good realism and justice to deep & powerful vocals. Treble detail all present and accounted for. Handles delicate or thunderous passages equally well. Slightly metallic reverb and a little bit soulful/gritty/smokey – which adds interest. Recessed mids may leave some people cold. Super all-rounder. Bass is articulate but a little lean or somehow lacking weight. Not as delicate or sweet as GEC 6080. Could see people loving or it or saying wtf. Too expensive by a long shot.

    I might still take a Tung-Sol 6080.

    Treble: 8.5
    Mids: 8.5
    Bass: 7

    Overall performance: 8/10
    Value for Money 6/10


    [​IMG]

    [​IMG]




    Tung Sol 6AS7G

    Price: £30-£40 each
    Availability: average


    Also appears under Chatham label. Those labeled 6520 may also be a “select” version of this tube. Notable construction details include contrasting silver fins on plates, which protrude through top and bottom mica.

    Probably my favourite tube and right in the tonal sweet spot for me. i.e. somewhere between 5998 and RCA 6AS7. Gets you 80% of the sparkle, resolution and balance of the 5998 with added juice in the mids. Mid-range champ with impressive and eerie holographic guitars and vocals. Excellent-3D-realism in percussion. Doesn’t give up too much in detail but is generally softer all around the edges. Fluid & effortless but not smeared. Staging not as wide as the best-of-the-best but trumps all in depth and texture. Behind 5998 & GEC6080 in pure technicality but ahead in overall cohesion and emotional engagement. Slightly rolled at the top. Respectable low-end. For £30 kills everything else in that price-bracket (and above-depending on tastes).

    Treble: 7
    Mids: 10
    Bass: 7

    Overall performance: 9/10
    Value for Money 9/10


    [​IMG]




    GEC 6AS7G / A1834

    Price: £100+
    Availability: poor

    Holy grail for 6AS7 rollers. This one is 1950s Hammersmith. Sounds a little more full-bodied and convincing than the GEC 6080 but perhaps falls behind in imaging and delicacy. Has a sense of effortless “purity” – whatever that means :-/ . Vocals smooth and totally clean. Treble finesse and extension is up with the best. Hard to fault in any area….

    Finding it hard to get too excited over this tube vs the price and due to slight sense of limpness and absence of bite vs my high expectations. Grain-free. Somehow seems a little muddled at low volumes but opens up nicely at higher (more than I like) volumes. Winged-C has wider soundstage. TS-6AS7G more holographic and immersive. Silly prices. Happy to skip this one, buy a TS-6080/6AS7G and sleep well.

    Treble: 8
    Mids: 8
    Bass: 8

    Overall performance: 8/10
    Value for Money 3/10

    [​IMG]

    [​IMG]
     
    Last edited: Aug 27, 2017
  7. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    I've officially got the Crack 2 up and running. I've got a possible ground loop problem that I'm still trying to fix, but initial impressions are extremely positive. Pictures to come once I get everything working properly.

    The amp is a fantastic pairing with the 600s, but sounds even better with the 650s. I have a SuSy Dynalo sitting next to the Crack 2 and the differences between them are pretty startling.

    I'm going to be super happy with the Crack 2 as a change of pace amp once I get all the kinks worked out.
     
  8. keanex

    keanex Martian Bounty Hunter - Friend

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    Ah deletetheweak finally completed it? Last I saw it it was without a case! lol seeing him use it without a case was hilarious.
     
  9. OJneg

    OJneg The Most Insufferable

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    Great comparison Jeb! I definitely notice the somewhat lean sound of the 5998. Looks like I should definitely try the Tung Sol 6080 before I write the 6080 tube off. Also looks like the 6H13 is a tempting option.
     
  10. velvetx

    velvetx Gear Master West/Vendor Spotlight Moderator

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    How hard was it to build?
     
  11. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    It isn't easy as a first build. If you've never done anything before I still think the stock Crack is the way to go. Add the speedball to it once you are done.
     
  12. Jeb

    Jeb Friend

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    Cheers @OJneg - yes I like the Tung Sol 6080 a lot ! Agree about the 5998. I know Doc B has been known to pair it with something richer in the other slot -like a Mullard CV4003 - I could see that working well to flesh things out.

    I spent some time with a load of 12AU7s etc and will put up some pics/thoughts sometime soon.

    I must say the Crack really sounds extra good with nice tubes even though it's also totally enjoyable with the stock ones. It's nice that the kit comes with NOS tubes. I'm not dead set against modern stuff, but I tried a couple that were pretty nasty.
     
  13. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    [​IMG]
    [​IMG]
    Ground loop issues solved.

    Really fun little amp. I'm looking forward to getting to A/B it with an original Crack/Speedball.

    It is amazing how different it sounds from the other amp I have in house at the moment, the SuSy Dynalo. If I had to pick one, it'd be the Dynalo, but I don't and won't. The Crack 2 is a fantastic change of pace amp and makes for a super relaxing pairing with the HD650s.
     
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  14. Jeb

    Jeb Friend

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    ^ looks great ! Case looks v. neat too. Plenty of space for modifications under there - if you were so inclined.

    Comparison with Crack 1 would be really cool when you can.
     
  15. TMoney

    TMoney Shits on SBAF over at Head-Case to be cool

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    Will do!
     
  16. ohshitgorillas

    ohshitgorillas Almost "Made"

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    Has anyone tried a 6SN7 as the input tube via adapter? That's the tube roll I'm most curious about, although the RCA clear top and Amperex are both very solid performers.
     
  17. Hands

    Hands Overzealous Auto Flusher - Measurbator

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    Yeah, I have that on my Crack. Works fine. Not sure about the Crack 2.
     
  18. Cspirou

    Cspirou They call me Sparky

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    The Apex Teton is a 6sn7 + 6080 amp. I believe quite a few people heard it at Big Sound with Innerfidelity.
     
  19. Jeb

    Jeb Friend

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    12AU7s & Variants

    I decided to do some quick comparisons of 10 tubes from the 12AU7 family that I already had from another amp prior to buying the Crack. I also tried a 6SN7 + adapter at the end, to add some context.

    All impressions with stock HD-650 & Rega DAC. The Rega DAC is all I have. It's on the warm side and suffers from a slight congested feel among other things. I Used a multi genre playlist.

    Conclusions:
    • The Crack is very nice with stock tubes
    • The Crack is more-nice with betterer tubes.
    • Excessive tube rolling can be ruinous to the enjoyment of music, life & tube sockets.
    • There are many highly average 12AU7s (tube-sidegrade-purgatory) but a few that are very good (worthy upgrade)


    Siemens Silver Plate ECC82 *worthy upgrade!

    Price: ~£30
    Availability: not great

    Harder-to-find distinctive silver (Nickel) ladder plate from Munich factory, 1960s. Expansive, lively, airy and refined sounding but not without a respectable (but lesser) degree of euro-style warmth/sweetness – makes this a fairly unique proposition. Treble sparkly & perhaps best of all for extension. Makes 650s sound quite impressive/resolving/focused. Perhaps light in bass weight for some but still articulate. Needs an output tube with substance to add a little more meat to mids/vocals and mid-bass presence. Need to avoid over-brightness. Wide but perhaps a little flat in depth - still plenty for me. Always sounds in control. One of my favourites. Shiny.

    8.5/10 - worthy upgrade

    [​IMG]





    RCA "Clear-top" 12AU7

    Price: ~£10
    Availability: excellent

    Light grey ladder plate, rectangular side getter from RCA ‘70s. Popular choice for Crack but I’m not a fan. Forward sounding & lacks separation, imaging & finesse. Guitars unnaturally piercing at times. Fuller bass than Siemens but somewhat flabby. Congested and muddled through the lower mids then bright & aggressive further up, combined with narrow/forward sound – makes for uncomfortable & disjointed listening for me. Sounds a little out of control compared to the best of them.

    4/10 - sidegrade

    [​IMG]





    Psvane 12AU7 –TII

    Price: ~£55 pair
    Availability: excellent

    Modern production gold-pin Psvane. Nothing against modern tubes but this is not good in comparison. Muddy & ill defined. Pathetic mono-note bass. Tin-can treble. Congested & unnatural. Poor sense of scale . Harsh, grainy & fatiguing. To be fair, mid range has reasonable depth. This isn’t cheap and there are many better easily available NOS tubes for less. Even the re-issue stuff from New Sensor is better. Perhaps one day these are the tubes I’ll have to use. But not yet. Not yet.


    2/10 - downgrade

    [​IMG]





    Philips ECC82 (Holland)

    Price: ~£20
    Availability: poor

    The good stuff from Dutch factory, 1960s. Grey ladder plate with dual post halo getter. Many different rebrands for re-sale throughout Europe/US (incl. Amperex, Mullard, Valvo, Philips Miniwatt) so look around & check codes for delta symbol (factory = Herleen). Not sure if these are fully comparable to the popular “Bugle-Boy” run that came from the same factory & were relabelled for sale in US as Amperex - but the internals look v.similar.

    I can see the attraction of these. Fundamentally warm. Smooth but pleasantly detailed. Clean vocal. Decent mid-range depth. Holographic with average width. Plenty of twang to guitars. Bass is boosted but quite mushy – not awful – though definitely degrades the attack and bleeds into mids. Super treble – believable, smooth and extends well. But meh - Overall, dynamically somehow disappoints a little. Seems slow. Won’t offend anyone, but might get boring due to lack of guts (attack). Solid choice for a warm tube if you can handle the trade-offs & slightly soft & bottom-heavy sound which unbalances an otherwise decent tube.


    6.5/10 - sidegrade


    [​IMG]





    Mullard CV4003

    Price: ~£30(eBay)
    Availability: average

    Widely praised British military, ruggedized, 12AU7 variant. Grey “box” plate, single post halo getter. This one 1980s. Hailed by many as the only 12AU7 you’ll ever need. Classy, full-bodied, mid-centric, mid-range king. Guitars & vocals “natural”, smooth & second-to-none. Actually, vocals are brilliant & a little forward. Highly cohesive sound & great all-rounder. All slightly blended/rounded but not crazy-gloopy & maintains above average impact, nuance & plenty of composure. Dynamically bests the Dutch Philips. Low-end better controlled but still not stellar. Not wide or expansive.. Immersive. Never tiring. Prices are beyond stupid – especially Upscale Audio. Prefer eBay. Listened to playlist twice, just for kicks. Top 3 tube.

    8/10 - upgrade

    [​IMG]




    CBS Hytron 5814a

    Price: ~£20
    Availability: Poor

    US tube from mid 1950s with black-plate, bent & slanted rectangular getter. Not the same as CBS-12AU7. Less warm than Euro tubes. Wider, with better balance & bite than Mullard. Notes still robust and convincing and overall just as cohesive albeit in a slightly different & drier flavour. Crisp with good clarity. Dynamically more alive & well separated. Less sweet but a long way from thin. Tighter bass. Good rumble. Seems to get the head nodding.. Very convincing 3D depth & texture in the mids. Nice treble decay. Very cool sounding with slight nostalgic “smokiness”. Bargain but annoyingly rare. Perhaps a bit dry & nasal for some. Also have some labelled Hytron from early 50s – still v.good but a tad thinner.

    8/10 - upgrade

    [​IMG]




    CIFTE 12AU7

    Price: ~£25
    Availability: average

    Early 60’s French military valves with halo getter and distinctive hole in the plates. Also appears under Mazda label, I think. Warm but delicate up top. Seems quite uneven with strangely recessed mid-range frequencies that had me straining for detail. Compressed. Timbre is flat & hollow. Otherwise all a bit limp. Bass weak & seems to distort slightly. Disappointed by this one – I used to love this tube for its sweet, articulate & inoffensive sound - but don’t much like it in the Crack for some reason.

    5/10 - sidegrade

    [​IMG]




    5814A Sylvania & 12AU7 Sylvania (stock)

    Price: ~£10
    Availability: very good

    Sylvania JAN 5814A - Widely available toughened US Military tube from mid 70s. Many similarities with stock Sylvania 12AU7, but sounds a little clearer, crisper & better separated. Like a CBS-Hytron 5814-lite. Other than slight bass-boost vs stock tube remains fairly evenly balanced throughout & cohesive. Decent clarity (6/10). Lacks the finesse and depth of the CBS-Hytron. Can also be a little raw & artificial sounding in midrange. Upper mid/treble timbre somehow seems rough. Vocals sound hard & slightly robotic. Guitars a bit lifeless. Grainy. Decent tube – still better than the Psvane but off the pace vs the best NOS offerings.

    May as well mention the stock Sylvania (relabelled for Hammond) 12AU7. Different spec but construction looks almost identical. For sound, see above – v.similar but slightly more muffled. Lacks a bit of focus but therfore avoids some of the roughness of the 5814A. Both make you appreciate the benefit of the nicer valves but also unlikely to stand in the way of enjoying the amp.

    5.5/10 - sidegrade

    1) 5814A
    [​IMG]

    2) Stock 12AU7
    [​IMG]





    Telefunken 12AU7 / ECC82

    Price: ~£40
    Availability: average

    West-German ribbed plate from 60s with chunky halo getter. Look for the Telefunken diamond <> on the base for authenticity. Also available as smooth plate which may be better/different.

    Expected it to sound thin. No. Very difficult to make the Crack/650s sound thin. This Tele’ is tonally remarkably even. Genuinely freaky sounding tube. Smooth, clean & 3D midrange with outstanding detail & realism. Especially vocals. Imaging excellent. Everything seems like it has space to breathe, extend and decay. Treble airy but still smooth – slightly lacking in sparkle/extension vs the Siemens silver plate. Can’t shake the feeling that this sounds slightly cavernous & echoey with bizarre reverb/ghosting. But I like it. Lacks some inner warmth or fluidity vs Mullard or Philips (& Siemens) but also doesn’t sound too analytical or dry. No harshness. Very atmospheric, “live” sound. Would advise to pair with an output tube that is “organic” sounding to balance Telefunken weirdness & possible absence of a human soul.

    One of the few 12AU7s that really stand out, although lovers of the lush might want to look elsewhere.

    8.5/10 - upgrade

    [​IMG]





    Vs Sylvania 6SN7WGTA + Adapter

    I only have one 6SN7 - a brown base Sylvania 6SN7WGTA, which was not expensive (£25) but I understand is a "decent" tube if you're not going to go crazy with the rare breeds.

    I have seen these described as perhaps a little "lean", "dry", "fast" or one of the more "transparent" 6SN7s - I can't speak to the truth of that but vs most of the 12AU7s this 6SN7 still sounds pretty soft and rounded in comparison. It does sound good. Lush, smooth, liquid and effortlessly listenable. Staging has good depth but all a bit muddled. Everything is a little more inflated, which impresses initially but subsequently feels too tubby and out of balance for my tastes. For me it would be a shame to lose that dynamic, punchy edge. Slightly tramples the spirit of the Crack.

    Take the Mullard CV4003 - now that's a warm tube - but tonally it still remains much more even and seems to offer a higher degree of focus than this particular 6SN7, which is altogether richer, blended and boomier.

    It's undoubtedly better than many of the tubes I tried, but for me, the very best of the 12AU7s I used probably still have the edge. No doubt superior 6SN7s exist.

    7/10




     
    Last edited: Aug 27, 2017
  20. ohshitgorillas

    ohshitgorillas Almost "Made"

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    Interesting. My impressions of the Clear Top and Amperex 12AU7 are quite different. I find the Clear Top RCA to be very dynamic and resolving with excellent tonal qualities, and I find the Amperex to be very sweet and forgiving with great soundstage. I guess how they ultimately sound is also going to depend on the power tube used... is that the GE brown base 421A or whatever it is? The one that's crazy expensive and hard to find?
     

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