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    Preamp tubes

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    ugabuga

    Posts : 3
    Join date : 2018-05-13

    Preamp tubes

    Post by ugabuga on Sun May 13, 2018 8:59 pm

    Hi, new to the forum here.  I purchased my HK Grandmeister deluxe 40 little over a year ago.  Love it, but having a few issues now with it making sounds by itself, even in standby.  Also loud noise when changing presets especially if there was a wattage change with the preset.  I changed the power setting to global to prevent the wattage change.  It was making the noises for a little bit than slowly got better after several uses, and stopped all together and worked great.  Now the issue has returned.  I seen a flicker of light coming from a power tube when the noise was coming out, so I've ordered a new set of power tubes hoping that's the issue. I don't want to send it in for warranty just yet as the tubes only have 90 day warranty, so I'll try that first.  I went with Electro-Harmonix EL84.  Seem to have some better reviews than JJ and sovtek.  I know they make great pedals.  Groove tubes seemed little pricier so didn't look into reviews for those.

    My question though is about the 3 12ax7 preamp tubes.  I'm new to tube amps.  For the 3 preamp tubes, I notice that the tube on the right is a tall blue tube and looks different from the other 2, but it says that it has 3 12ax7 tubes.  Why is the one way different than the other 2?  I also noticed the left 2 say 12ax7b.  If I replace those, do I need to find 12ax7b?  What is the 'b' for?

    Thanks in advance, help is greatly appreciated!
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    JonnyNonsense

    Posts : 67
    Join date : 2017-06-19

    Re: Preamp tubes

    Post by JonnyNonsense on Wed May 16, 2018 5:36 am

    I believe all the preamp tubes are the same (although you might order a 'balanced' one for the first tube). It's just that the first tube has a different kind of shielding around it or something.

    I guess if you have had it for a year, that means your H&K Warranty has expired? I can't remember how long it's valid for. If it's still under warranty, you want to be really careful when changing the tubes. There is a tag inside the amp that will break if you fully remove the housing, and that invalidates your warranty.

    There's a youtube video that shows you how to change your tubes without doing that though.
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    bordonbert

    Posts : 1015
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: Preamp tubes

    Post by bordonbert on Wed May 16, 2018 6:29 am

    Hi Ugabuga, welcome to the site.  If you want details on valve stuff go to the GM36 forum and look there for the Tube Swapping Thread, you'll get all that you want and more.  Make sure to read around the middle of Page 5 Post#122 onwards for a bit and have a look at Page 6 Post#141.  There is a comparison there from VoodooJeff between JJs and Wathens.  The Wathens are apparently made of Unicorn horn in Hogsmeade just down the road from Hogwarts School by qualified wizards from Harry Potter's class working under Hermione Granger and they cost currently around $140 per 12AX7!!!!  (That price is absolutely true!  Check it on the Wathen Valves site.)

    The differences between valve makes are hyped and overstated.  Period!  It's marketing speak in order to shift more valves.  Any differences between the same valves from different manufacturers are very subtle and can hardly be heard in a live environment.  If you are a bedroom virtuoso then you may be able to hear a slight difference if you are specifically looking for it.  Playing along with others, not much of a chance at all?  What people fail to realise is that these valves were originally designed for radio work, not audio which they just fell into as the cheapest and most suitable available.  They have characteristics to which they all must conform to be given their type designation and their frequency responses all extend up to the Megahertz region making some of the claims of differences in tonal quality a joke.  Not much chance of much difference at around the 5-6kHz upper level we work to.  If there is a difference it should be obvious when put on the bench and tested rigorously with good quality electronic test equipment.  As yet, no one has to my knowledge managed that and if they had it would be front page news!  Yet they all still claim it is like night and day.  I and a few others around claim BS!  My advice, don't be fooled, and if you compare types make sure you know the limitations of just swapping with a couple of minutes in between listening (10secs max and the ear and brain "recalibrate" and the test becomes nonsense as you hear what you want to hear) and be brutally honest with yourself.  Don't listen trying to hear a difference, try it the other way around, listen to NOT hear a difference and see if it surprises you.  If it is as obvious as people maintain then it should, repeatedly.

    Balanced valves are only of use in the Phase Inverter stage of some amplifiers.  They make no difference to the preamp input and amplification stages at all.  The triodes in these are used independently in their stages.

    The original valves in the H&Ks used to all be the same.  They had "China" stamped on the front down towards their bases beneath "12AX7".  Looking on the H&K site I can see what you are talking about, the GM40D seems to have a different set now.  They are marked 12AX7B and are missing the Chinese designation.  The "B" is supposed to denote a "Shuguang's better selection item versus their 12AX7 or 12AX7A" according to TAD.  "It's better", very helpful and informative especially when it is listed in full but with the ordinary 12AX7 down at the bottom of a list of equivalents.     The valve on the right is the input valves and is screened by a blue metal can to prevent noise pickup.  The input stage is more susceptible to that than the others as the signal is at a lower level there.  If you twist the blue metal cap round it should spring off and you will see the actual valve underneath.  My bet is that it will be the same as the other two.  If it is different in any way it will most likely just be a low noise type of the same 12AX7.  That is the main area where there will be differences between valves, (but not necessarily manufacturers), some are less noisy and some are less microphonic.  All valves are microphonic, some are just more susceptible than others.

    The idea that there is very little difference between different manufacturers' valves of the same type is "Hint 1".  You can't even test it properly without engineering lab conditions to make the change instantly switchable.  "Hint 2" is one which you are unlikely to hear in many other places it has become so widely believed by the untrained.  Don't be tempted to swap out for different valve types like the 12AT7 12AU7 12AY7.  These are definitely NOT equivalent valves, they are very different and screw with every aspect of the stage design to the point where it may even cause damage, (though damage would be pretty rare).  These are often pushed as a "lower gain equivalent".  Anyone who quotes you the term "gain" doesn't know anything about designing with valves!  The parameter does not exist.  There are a number of interconnected parameters, Amplification Factor (The one that is often thought of as "gain" but which isn't), Anode Resistance and Transconductance, and a change to any one affects the others.  You cannot lower the value of Amplification Factor without screwing the other values to places where they are an appalling fit in any stage not designed specifically for that valve type.  It is much more complicated than just "lower gain".  Why pay money for an amp which a good expensive designer has spent months setting up to toss his work out of the window by putting in the wrong valve type and messing up everything he was so careful to get right?

    Anyway.  You should be happy with your Electro Harmonix when they arrive, they are a decent valve.  If you read the Tube Swapping Thread you will find that other makes like JJ are also good valves, in fact most of us here seem to use JJs and are very happy with them. The reviews are based on hype!  No one ever compares the valves in anything like an accurate rigorous way and never in a real live situation.  When you make money from selling valves or writing reviews you have to justify buying the valves or reading the reviews to your public.  Have you ever heard a valve supplier or reviewer say "well, there's actually not a lot of difference I can hear"?  It goes against the idea of swapping out your valves and that is lost revenue.

    The "magic mojo" component doesn't exist!  Not in any area.
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    ugabuga

    Posts : 3
    Join date : 2018-05-13

    Re: Preamp tubes

    Post by ugabuga on Wed May 16, 2018 11:44 am

    Thanks for the replies, tips, and videos.  Good to know that its just a covering over the tube for shielding purposes.  It has a 2 year warranty, so I'll be extra careful to try and not break the seal.  I hate to pay $50 for shipping it in and have it be the tubes.  I paid less than that for the 4 tubes.  And then have them charge me a ridiculous fee for changing the tubes as they only have a 90 day warranty on tubes.  I'll find out tomorrow night if this solves my noise issue.

    Thanks again.
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    JonnyNonsense

    Posts : 67
    Join date : 2017-06-19

    Re: Preamp tubes

    Post by JonnyNonsense on Wed May 16, 2018 11:49 am

    Cool. Definitely look up that video about not invalidating the warranty. I think somebody demonstrates on a Tubemeister. Basically you have to *not* unscrew the sides fully to avoid breaking the seal - it's easy to do but I really recommend watching the video.

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    bordonbert

    Posts : 1015
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: Preamp tubes

    Post by bordonbert on Thu May 17, 2018 5:28 am

    Good advice Jonny, it's an easy process but important if the amp is still in warranty.  To summarise...

    On each end cheek, remove the top two screws and the middle level rear handle screw completely.  Leave the front handle screw alone, it only holds the handle onto the end cheek.  Then loosen the bottom two screws only a turn or two, they are the ones with the anti-tamper indicator.  The end cheeks will then gently pull outwards enough from the top to be able to carefully remove the top cover.  Be careful with the LED strip power cables running down the right side edge of the front panel as you look at it.  These are fairly fine.

    When you are refitting take care to get the LED strip in place on top of the acrylic front panel correctly with all of its clips in place before refitting the top cover and tightening any screws.
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    ugabuga

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    Join date : 2018-05-13

    Re: Preamp tubes

    Post by ugabuga on Fri May 18, 2018 8:41 am

    Put the new EL84 tubes in last night. So far, so good. Sounds beautiful. Not sure if it sounds any better than the amp did brand new, but does sound better than before replacing the tubes. The problem was a little intermittent before, but I should know by the end of the weekend. Now to decide if I want to replace those china preamp tubes. Thanks for the help.
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    bordonbert

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    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: Preamp tubes

    Post by bordonbert on Fri May 18, 2018 9:32 am

    Good news on that one Ugabuga, glad they turned out well. Good to hear you're keeping a critical open mind when you say that it may not be better than when new. A lot of people actually prefer the sound of those Chinese valves but are almost afraid to say they do for fear of ridicule. Whatever you decide to do about them make sure it is based on your dissatisfaction of the amp's sound. Considering changing them because you are unhappy with the sound is sensible. Doing it just because you just think there is something golden to chase and it may get better isn't, in my book.

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