The Tube Swapping Thread

.............I try my hardest to stay out of tube debates and elsewise related topics. It`s a lot of hoodoo mysticism (yeah, yeah. The irony from a guy who`s nickname is Voodoo. LOL). I have swapped tubes of varying combinations into and out of a dozen amps over the years to little more than subtle results. Yes, sometimes the subtlety is all it takes to turn an "almost perfect" amp into blissful sweet perfection (my Legacy 3 was a good example of that), but most times it`s nothing more than a placebo effect. As a fairly new GM36 owner I have read that it tends to respond well to tube changes. My one complaint about the amp is that it can be a bit brittle and cold, so I`m going to swap in a set of JJs (IMO the ONLY brand that has any level of reliability and consistency. Even GT became a "slap our logo on some cheap a$$ chinese tubes" company a decade ago. I`m going to grab a set of Gold Pin 12ax7s and hope they smooth out and warm up the sound a tad. The effect of power tubes is quite literally wasted until the amp is played in the upper 30% or so of it`s output (read: LOUD) so I`ll worry about those in a few months.

Absolutely with you on the sceptic bench Voodoo, (as I've said before ad nauseam). I won't make a claim until I've tried it back and forth as many times as possible, and even then I'm still dubious and uncomfortable about accepting it! I do consistently prefer some tube swaps though.

The point of them is that the more basic circuitry of valve (I'm British!) stages compared to solid state ones is influenced more by the device characteristics and less by the circuit topology.  And most recommended valve swaps are from a device which the stage was designed to match to a differing device that has totally different, sometimes even conflicting, parameters.  Just as I pointed out for the 12AX7 -> 12AT7 swap that most people start with.  It's not surprising they sound different, the unchanged supporting circuitry is unable to cope with the differences in a lot of ways.

EDIT: I'd just add... It's a shame that you stay out of those debates. The problem is that most people who think like us do just that. That's why many of those who post, with no real understanding and even precious little experience of what they are pushing, can make the mythical side of it stick.  The people who could make the case for there being too many myths and legends in the issue are rarely heard.  It all comes down to Physics in the end, and the "mojo magicians" don't want us to believe that.  (Else where would their next SUV come from? )

And I bet here and now that your amp does sound smoother with the replacements! Your description of cold and brittle is exactly my own when I first got mine, (and the TM36 I already had). I found the speakers are a MASSIVE factor there. Vintage 30s - NO, G12M Greenbacks - Yes! It developed walls at the bottom end and a smooth ceiling on top. The valves just finished off the plastering.

  Well!  I've had a couple of replies on the H&K Facebook page.  I have to say it's impressive.

H&K Facebook wrote:Hi again Albert. OK, so we've been told from a technical standpoint this would be safe, but our tech expert also said: "but if it sounded so much better, we would have built it in anyway..." So make of that what you will!

I thanked them and said that there will always be some owners who would prefer to tweak their amps to get a sound they prefer.  They immediately came back with:

H&K Facebook wrote:No problem, and we will pass your thanks on. The thing about tone is: it's totally personal. Like you said in your originaly message, a change of tone might be 'preferred', but is it actually 'better'? That's an answer that's different for everyone  

Our two cents, though: we obviously put in tubes that we think sound amazing. There'd be no point otherwise. But we totally understand that there are tube amp purists out there who have their own favorites and want to change things up a lot, and that's why we have systems like Tube Safety Contol, so they can change things round easily and not have to worry about tube biasing, etc.

It's all in good fun! Enjoy whatever tubes you decide to go with in your GM36, and if you find some geat new ones, let us know... We're always interested to hear what you guys think sounds good, and we might even take the info into account for future amps  

You can't get better than that.  For a design team to respond and tell you that a non sanctioned change is at least safe is great service.

So those of you who prefer the potentially thinner sound of 12AT7s, it's a good swap.    This means that that 5751 alternative I found should be even better!    Personally, having seen what they cost, I'm trying to get my hands on a couple of 5751s as a much closer match to a "Lower Mu 12AX7".  (I have even read somewhere that they are in fact low mu reject 12AX7s). That way the voltage and bandwidth considerations stay virtually in line with the originals.  I wouldn't want the potential raising of the lower frequency cutoff that a valve with much lower plate resistance like a 12AT7 could bring to it's stage.

Hey bordonbert that's a good responce from hk I got my tubes 2day went with quad matched jj el84 in the power stage and 3 jj 5751 and the fizz is so much better I can crank my amp a bit more as well I won't comment on the tone cos I'm a total noob but I will say it sounds a lot smoother and the most important part for me a lot less fizz

Stapletongas I got my tubes same as your first setup and I can confirm what you said on your first post cheers mate next stop a Marshall 1912

H&K do a fine job of interacting with their users. I really appreciate that about them. It`s honestly what makes me want to endorse the brand.

Be very selective with your speaker choice Luke. You really need to hear the match with a GM36 before you put any money in. There is a fair bit of discussion on the forum re speaker choice, most people find that their amp is very sensitive to it. Look on the TM36 forum as well and the 112 and 212 forums (should that be fora? ).

Personally, I started with 2xVintage30s because they were cheap but good quality. It was awful! They were wonderfully loud but the balance ripped your ears off. They seemed to feel very light in the bottom end and they really emphasised that spiky shrillness that can come out in the top end, (just what you are trying to solve). I replaced them with two G12M Greenbacks and it all went away. It was sweetness and light. The bass started to come through and the top end smoothed out beautifully.

But don't just go for what someone else has told you is a good choice, that's just a starting point. You really need to listen before you make a decision and wad up or you'll end up spinning around the plug hole as so many of us do with your money being sucked down the drain in the middle.

Hi bordonbert I'm guns take your advice mate I tried googling g12m after you first mentioned them on the other thread and all I could find was the actual inside of the speaker I realise that g12m is the name of the component and not the cab is there any cabs pre built with them already in that you could recommend 4 me to try I tried looking but struggled to find any thanks for all your help mate I know I'm properly asking a lot of stupid questions but it's all new to me

It's a difficult one Luke there is so much choice. You can easily end up like the Greek donkey that was stood between two baskets of carrots and starved to death! I started with a couple of cheap 1x12 cabinets loaded with the Vintage 30s. They are good speakers but I didn't feel they were a good match for the H&Ks. I swapped out the V30s for the couple of Greenbacks I picked up and the cabs were fine so mine are replacements. Having a quick look online it looks like there are no Marshall cabs with G12Ms in them as standard. I can't find any other well known cabs which use them either.

Maybe someone else will be able to point us towards a couple. That said there will be others who know a lot more about the various driver models' sounds than me and could maybe recommend one or two which give you the same fuller bass and smoothness of top end you need.

The differences in this sort of thing are often hyped up to be life or death issues. In truth, just like Voodoo said above, while it makes a difference it's not something to jump off a tall building over. Take your GM36 to your nearest good gear shop and ask to play it for a while through a couple of their likely cabinets and see for yourself what matches and doesn't. They'll love you for doing it even if you don't buy anything because it gives their shop an air of business! You don't even need to know what the drivers are, if it sounds right to you then it IS right. It just takes confidence in your own hearing and knowing what you want before hand so you don't get steamrolled. If you don't like something say "No" and move on!

Somebody wise once told me that, when you are playing to an audience, there are two separate parts. There are the players, who spend their time criticising your gear, criticising your image, criticising your material and criticising your playing technique. Then there are the listeners who are just getting off on the music you play. What do you think the balance between them is? Whose opinion iis more important to you? Those cabs I mentioned that I bought were Harley Benton from Thomann, and they are virtually free if you take into account the cost of the driver in them (which I had to sell on). So they are cheap as anything. My pedal board is a neat and tidy two tier wooden diy job, I won't pay a small fortune for a couple of pieces of welded scrap steel! But they both work, and they work well, so I'm keeping them! I often see quizzical looks and raised eyebrows from the other muso "experts" out there, but the main body of the room just listens to the music the band makes and doesn't see anything like they do. Don't worry you might end up with what some people consider to be the "wrong" gear, as long as it sounds right to you then it can't be wrong at all.

Cheers bordonbert and thanks for all the advice I think like you say I'm just guna have to go to a shop and get stuck i feel like iv got a bit of a head start with every thing iv read on this fourm it will probably be a few weeks b4 I get dawn to a shop (I live on a farm in the middle of nowhere) and the nearest big guitar shop is about half a day away but when I do irl report back thanks again mate

Great thread, and thanks to all who put in the time and effort and shared their results. It doesn't get better than this kind of information sharing.
That said, I was happy with the way my GM36 sounded from the outset, and have read all the posts to learn more; learning never stops.

WRT cabinets; I will read the cab threads again, and change my post to accurately reflect what I am using, if anyone cares.
One thing in particular is my GM36 sounds amazing with my Marshall 1960A cabinet, a 4 x 12 with Celestion G12T-75W's.
And it sounds amazing, repeating myself.

I like it much better than the H&K 212, which if the 1960A wasn't sitting next to it I would have been happy with.
It just shows A/B comparisons are the way to go.

So, I learned a lot about tubes, learned to be cautious but not frozen - fearful of change, and that most of you all may have better ears than I.
Time well spent.

What type of music are you playing Mike?  It struck me a while ago that the voicing for the GM36 leans towards high gain power rock at the least.  It is a versatile beast but you have to be very specific if you want anything less - well - raucous!    It's my feeling that that's where the tube rolling and speaker choices become so critical.  I think the design thinking may be that if you cater to the highest gain needs then the lower gain needs are catered for by just backing off, at least a little.  The channels do seem to be voiced differently which is most likely a mechanism to set it up in a more universal fashion, but it doesn't always work that way unless the speaker choices match the voicing you want to adopt.  Just backing off the higher gain channels can make the amp controls clumsy and critical to set up for the cleaner user.  Using the Clean channel for cleans and the Lead channel for driven leads is not always the best way.  There are threads here where people are reporting great tones achieved by backing off the Lead and even Ultra channels to a clean sound.  The channels are no doubt inherently different tonally but using higher gain channels to approach clean sounds means having very little usable rotation on the Gain which can make it fiddly in use.  I find the tone controls more subtle than almost every other amp I've used, so much so that I have started using those higher gain channels with their different sound backed off to get at some sounds I like.

You will find earlier in this thread that I asked H&K about the reliability of tube swaps to lower gain types.  They confirmed that there should be no reliability issues, (within reason of course), but the tone of their reply suggested they were a bit mystified as to why we would want to do it as they had spent time carefully voicing the design themselves.  I have no doubt that is true, but it made me think there is an element of them having optimised it as a high gain unit originally.

Having put in a lower gain Mullard 12AT7WA in the V3 PI slot, I have dropped my gain slightly and I planned to experiment with 5751s in the preamp slots too.  Then I reread a post someone had made complaining that the amp may have a solid state overdrive stage at its input.  They were horrified at this deceit by H&K!  The suggestion was that it was kind of like putting a Tube Screamer type pedal before the valves built into the amp. I actually doubt that that is the truth of it, and even if there is a solid state first stage, (other amps do exactly that), it would more likely be a totally clean gain stage to drive the valve stages following.  So "not relevant" I replied, and of course, if it sounds right the technology is largely a non issue.  But then I thought about it a bit and it occurred to me that it maybe isn't quite as simple as I first thought.  Changing the gain of each stage by valve rolling means that the balance of the overall overdrive/distortion mechanism changes, including the hypothetical solid state input.  Less gain later on in the valves may mean when you try to get more overdrive it may come more from the input SS block, (assuming it is really there).  The sound will change, perhaps significantly, with a drop in valve gain as more of the distortion is generated by that.  Some will like it but....

Maybe that is why H&K were a little miffed at the idea we undo their work to set up our own.  They have the full design details at their disposal and we are working blind by trial and error.

(For those who haven't read right through, see this thread, posts Nos 46/47 and 53 for more tech details and the H&K responses word for word.)

You nailed it in one; I play rip your face off metal.
No subtlety here.

If anyone is looking into new tubes, Tube Depot has got JJ EL84s for $9.95 right now.

Well, like many others, I find the sound of the GM36 very harsh and have been searching for ways to tame it for some time now. Unfortunately I have an Orange cab with 2 Vintage 30 speakers too! They are going to be changed soon. I have been running the amp with no presence and treble on around 2 for most patches. I finally resolved this week to try changing some valves. So having armed myself with the relevant information, reading this thread and other valve threads many times over, and following a call to the excellent Watford Valves I decided upon a set of JJ EL84's, a JJ5751 and 2 JJ ECC83s.

They arrived yesterday afternoon and I set about changing them straight away.

I started with the EL84's. Immediately I was very pleased with the results. I played the amp for a long time in this config and tbh I could have left it at that. Much more warmth, darker, creamier, fuller bodied etc etc. Breaking up earlier, more sustain etc. Very pleased indeed. Why didn't I do this years ago?

I decided to carry on. Taking the view that I could always revert to any combination but it would be good to see the effect of the other valves.

So the V1 next. The JJ5751, advertised as 15-30% less gain.Watford Valves had told me that they had tested these and that the actually gain reduction was around 10-15%. Again a big difference in sound. Even more dark, creamier etc. Similar effects overall to changing the power valves but more so. Again I was very pleased with the sound. There was still a clarity to it though that I liked. At this point I hasn't changed any settings on the amp/ I thought it only fair to leave it set as it started out to see the effect of all of the valves on my "go to" patches. So far so good.

Onwards and upwards. The V2 & V3 with the JJECC83s valves. Wow VERY VERY dark now! Maybe a step too far? I don't know yet. Certainly this needed to have some treble & presence reintroduced. I did that and I was still impressed though.

Overall the changes are stunning. I am more than pleased with this. I am will play the amp again today and I am sure that it will sound different. It always does the next day! I expect that I will need to experiment more with the preamp valves but the JJ EL34's are here to stay!

More later...

Interesting stuff....

So if I were to have a stab at trying some different valves which ones should I try replacing first? Sounds like JJ are the brand of choice.

I'm also in the UK so if any fellow Brits can recommend a good place to get them then please do.

I have the H&K TM212 cab so it sounds like I might get more significant changes if I were to try swapping the speakers?

I will be ordering some Celestion Greenback G12M speakers. They seem to be the speaker equivalent of the JJ EL84 valve!

Try a telephone call to Watford valves. They are really helpful and will outline several options.

Well worth a call imho.

Interesting to hear what you say about the 5751 swap.  I discovered that one when I was looking into whether a 12AX7->12AT7 swap was actually a reliable one, the info is somewhere on the site. (EDIT: Errmmm, it's actually in post 46/47 of this thread just over the page! )  The answer is, no it's not but you will probably get away with it.  It will work but you can't really predict all of the interactions which will be affected.  There are a number of important parameters which are not well appreciated and are VERY different between the two, and are also VERY significant.  There is so much more to a valve than maximum voltage, maximum current and gain.  For example, one is Anode Resistance, Ra, which relates to how well the valves match their loads and in turn affects the stage gain and frequency response.  Our 12AX7 and 12AT7 differ by a factor of 5-6X!  This is probably more of what causes the perceived differences than reductions in valve gain.

Then I found the 5751.  It is to all intents and purposes a 12AX7 with low gain.  It's Ra and other parameters are virtually identical to the 12AX7.  If you genuinely want to change out a 12AX7 to test just lower gain in your circuitry without affecting any other circuit parameters, the 5751 is THE starting point.  But the 12AT7 is the "goto" valve for swapping out for lower gain.  "Common Knowledge" says you do.



Just as a teaser to whet some appetites....  We all know of the potential valve swapping improvements and we know of the sensitivity to speaker drivers.  For those who find their H&K too toppy I have another trick up my sleeve I'm setting up at the moment.

Many people will know of the speaker "beaming" issue which has always plagued guitar amplification since speakers grew up and developed top ends, (ooerr matron! ( . )( . )   )  There are attempts to cure it which are based on that same "common knowledge", in other words "I don't know why but they are just true so there"!!!  There are many styles of "beam blockers" used, either home grown or which are on sale for silly money.  These may improve the overall sound by twiddling other factors but they sure as Heck cannot cure beaming to any degree.  The one approach which has engineering backing, (meaning is based on correct sound theory), is the Jay Mitchell foam toroids.  I have tried these on previous amps and, despite it being difficult to stringently test the results outside of an anechoic chamber, (at least a very open space would be needed to get reliable results), the impression they give me is that they work very well at improving beaming.  Unfortunately, by their action they also cause a darkening of the quality of the sound.  Note, this is a predicted part of the theory!  Now if we were to try these with a speaker setup for the H&K amps, that darkening of the tone would be a good thing for many of us.  I'm reviving my Mitchell Rings for a try at this.  I'll keep people up to date with what I find if anyone is interested.

I just received some Wathen Cryotubes to demo with the GM36. They are very expensive tubes, and the demo is going to be as A/B as can be. I`m going to record three passages, a clean, crunch, and lead part with the stock tubes. Changing absolutely nothing I`ll swap in the Wathen tubes and play the same passages. I`ll be using a direct track as well as a mic track panned hard opposite each other. I`ll post a video once it`s ready.

i haven't changed the stock tubes yet but i intend to do it with all jj's, hopping to see some improvement since the amp is relatively harsh.But i wonder why the support team from HK claim that they don't think there is a significant difference (i hope there is) from tube swapping, and why bother changing them since they have chosen the best according to them.Every user here including me think that the amp sounds relatively harsh, why haven't they done it from the beginning. Is there so huge gap between what we think mellow creamier sound and what others?

I think it may simply be down to the type of music you hear the amp playing in your head. If you're a metal head or at least very heavy in your tastes, then the amp will sound superb to you as it is. I have always said that being German the design team would naturally lean that way, (they love Hasselhoff and Sam Fox after all)! And if that is the case then they would have set it up to really shine in that field.

It has always surprised me that there are people who say they love it with Vintage 30s!!! I don't question their taste but I cannot see how they could possibly hold to that opinion when their ears have been sliced off like ham on a circular bacon slicing machine. And note that the TM 112 and 212 use....

If you want to use a GM for Clean sounding Country type music or even creamy crunchy Classic Rock you will need to get the valve/speaker setup to your taste and learn to use the controls with a degree of subtlety. Then if you have set it up to give a clean or mellow sound what happens to your heavily driven sound?

I agree with you but........from my point of view  there are several high gain amps out there which don't necessarily sound harsh at all.Let's say for example the jvm.Nice clean tones and great high gain tones without sounding harsh.A harsh sounding amp is a harsh sounding amp and that's a fact, for me who also own a fender deluxe and for a guy who owns a jvm etc and plays metal.The piercing highs and the sizzling tones don't mean that the grandmeister is more suitable for metal than a jvm imo.

I don't mean the tone makes it more suitable than say a JVM Ignantios, just maybe spot on what the designers think a metal amp should sound like. Unfortunately I have to disagree on one point. A harsh sounding amp is not a harsh sounding amp. It's a great sounding amp to someone who wouldn't describe it as harsh, just maybe as strongly overdriven. I'm with you, but it's all subjective.

hi All

really nice discussion in the last pages.

It was a long time I didn't post some news on the forum.
Well, I made some minor evolutions in my tubes:
- RTC 12AT7 WA NOS in V1 & V2
- JJ 5751 (70% gain of a 12AX7) in V3
- always JJ EL84.

I'm very pleased with the sound of my GM, but still found it a bit on the bright side (a trademark of the GM...that's clear).
As I have my beloved Axe Fx II (BTW I use too the AFXII only with a Cab Irs following my external Koch loadbox, to play the GM with other cabinets- great) too and use a buffer in front with nice addition in the tone.

I tried it in front of my GM and it was really great, improving the tone in the marschally side. Very nice, so now I use it always. But pay attention to the model I use for the buffer, a home made one (DIY), a Super Buffer AMZ.
I strongly recommend you build one (about ~30$ for components) and test. You might say, I don't need a buffer as i have just a 4m cable between my guitar and GM36, ok that's true. But in fact the buffer effect is really clear, giving you a more "meatty and creamy" tone, taming the high-side of the GM.

I have ordered jj el84 for the power amp section. I 'll do it step by step to see which effect on the amp has each step.I hope I'll see a big improvement as many have stated and not a subtle one.For the preamp section I 'll probably go with jj gold pin ecc83s in order to warm it more.I hope it won't cut down a lot of gain.