MAX Forty "Devil"

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Re: MAX Forty "Devil"

Postby Antti M. on Sat Jan 30, 2016 8:49 pm

Soo, this way? :Doh:

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Re: MAX Forty "Devil"

Postby Racing on Sun Jan 31, 2016 1:00 pm

Yeeeeeeeeeeep.....
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Re: MAX Forty "Devil"

Postby Antti M. on Wed Feb 10, 2016 5:26 pm

I've done now mods, except that golden rule and it became much better! :) Master vol I like is way better there between driver and concertina! This way I don't have to crank volume so high to get distortion if I want. But, it could be even better, although I have to draw the line somewhere... :roll: It's difficult to discribe how the sound should be different, but I believe the key is in the middle frequenzies, so maybe fine tuning James could be one thing? And other is that how it breaks/distorts, now distortions is "fine and thick", but I would like more rough, but still warm and smooth, like this way for example https://www.youtube.com/watch?v=LxF-SLHcotk or https://www.youtube.com/watch?v=DjB8Y1iVh1c. Near to dream amp would be that other channel could sound like these zztop examples and other channel more like this https://www.youtube.com/watch?v=WqfEcYnBvg8 or my third favorite kind of sound is about like this https://www.youtube.com/watch?v=gRZJWJxC684. Anyway, the baseline is that sound must remain clean always with distortion also, if you know what I mean. So that every note is clear and they don't just mix together. I hope you got the picture what I'm looking for ( don't know absolutely myself either, waiting to hear that perfect sound 8) )

I just don't know is it so simple to modify this to be like that or depends that sound about the tube types etc. also? And of course it would be nice to try this amp with another cabinet also, with some greenback elements or something...it may be that I change my cabinet later too. Anyway, one thing that I still would like absolutely change in this is that channel two is way way too quiet! I would like it to be as loud as channel 1 which is pretty loud. :thumbsup: But how can I do that?

BTW, did you receive the knobs?
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Re: MAX Forty "Devil"

Postby Racing on Wed Feb 10, 2016 11:50 pm

I certainly did.
You´re an honourable man Antti. Thank you.

So...got bitten by the mod bug huh? :lol: :lol:
Noone said it was going to be easy.. :lol: :lol: :jam:

Anyways. To get to the bottom of this we need to define a few things. I presume that you by now have gotten a feel for what various modifications will hand you,as far as sound and general practical results.
...and agreed. A MAX Forty with fresh EL-36´s that are handed ample signal..is one LOUD customer. No argument.

For tone.
Yes. If you compare the topology of your MAX with most other amps the thing with the MAX is that it basically only alters/forms tone at one point. Its tonestack and James (for respective channel).
Where you´re at right now is a sort of "in between" point. Most old school distorting amps uses a mere 2 gainstages and then heads into a phaseinverter of the longtailed pair type (LTP for short).
The cathodyne (aka concertina) phasesplitter might be simpler,but as you´ve gathered a concertina always has a driver stage ahead of it and as this driver stage is a common gainstage that lets you end up with all in all 3 common gainstages.

An imperative part here to free up tone,as you´ve started to push them 3 stages,is to pull back on plate/anode resistor value. The stock 220k setup is simply to much and will just cluster the sound palette while at the same time make the amp half soggy to the feel.
Replace all of them with regular 100k ones if you haven´t already.

Shaping tone can be done in a myriad of ways and what really sets the bottom line is the hardparts at hand. Ie,the actual tubes and transformers used. Both of the transformers of a MAX are of real high quality and dimensionb wise of ample sizes. The EL-36 tubes in turn is by FAR anything to shy away from. On the contrary. They´re good highpower tubes.
The onboard ECC-83s in turn...there´s miles to read up online as far as those.

The PT in turn will limit voltage to just shy of 400VDC as is. That is ample for most preamps and PI´s as far as rocknroll use,at least IMO. IOW..nothing to shrug at there either.

So what gives?

Well Antti. Most of this comes down to opinions and actual topology. A tube is a tube right?
No.
Tubes will take to their running conditions and that´s the lesson in all of this. All of us that spawn ideas as far as mods,and sorry to say rather few share those ideas willingly-which i think is pure BS,play around with topology and hopefully reaches some sort of solid standpoint for a given amp somewhere down the line.

I´ll try and explain this to you in a different way.

Let´s say that you and me are in the kitchen with a glass of whisky each and are bound to make bolognese. You know..spagetti..
Now..a few cans of crushed tomatoes...salt n pepper and ground beef might make it bolognese per se...but it won´t really taste worth a crap.
So.
Whisky.
We then start adding garlic..chilis...honey...basil...aso aso aso,and IF we get the proportions right we very well might have made this fantastic bolognese. A bolognese none of us want to stop eating of.

Putting topology together comes down to the same thing as that bolognese. The trick lies in the topology and setup.

If you want to check it out in a more hardcore way first thing on the agenda IMO would be to reset that concertina to a LTP instead. Or a paraphase..or even floating paraphase.
All of them,apart from the concertina,can make good use of a PPIVM setup,which will let you get to the good stuff without going deaf or becoming evicted.

The James,as the ONLY tone shaping part of that channel,have a rather profound effect as well but it will NOT add or distract to how "tight" the distortion is. It will impact what focus the freq involved has on the total outcome.
If rough is your wish it might be a good idea to check a paraphase out. Out of the three mentioned PI solutions it is by far the most "coarse" sounding. To get an idea of what it looks like google for a schematic of a Hohner MH-25. Doing so especially notice the trimpot for the farther grid. It´s there for a reason.
Running railvoltage for the PI will also have a rather profound effect. For three stagers i tend to end up around 350VDC-400VDC. However..if you remodel that phaseinverter as stated we´re in reality talking a two stager...
In that case try to get the entry stage to see 240VDC to 260VDC (according to taste) and serve the PI around 320VDC-360VDC (again according to taste).

For what it´s worth i´d in such a scenario add a pot of 1Mlog after stage two. Installed as a regular master as that in combination with the PPIMV pot aft of the PI will let you dial resolution in to hearts content.

Let me know what you decide on.
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Re: MAX Forty "Devil"

Postby Racing on Wed Feb 10, 2016 11:54 pm

Btw.
Getting the "Vox channel" up to snuff is mainly a matter of retaining signal/amplitude.
In short,look into how and why that tonestack is setup as it is. If not to your liking,or if you couldn´t give less of a rats ass for the Vox setup,try modding it to Marshall standards-of the JMP et al.
Same same.... :wink:
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Re: MAX Forty "Devil"

Postby Racing on Thu Feb 11, 2016 12:52 am

Antti....what´s more.
If you want more midfocus out of the amp only,then try this alter to the James.

Both inbound and outbound caps for the treble pot,replace both of those with a 1nF cap. Ie;1nF inbound for the pot and one 1nF outbound.
Put them values into TSC and see where it takes you. It´ll hand you a midfocused amp you won´t believe.. :wink:

..which brings us to what i do,amongst other trix. I install switches so the values of the James can be tossed and turned to hearts desire.
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Re: MAX Forty "Devil"

Postby Antti M. on Sun Feb 14, 2016 4:11 pm

Alright, let's begin questions with that phase inverter, here's pic of that Hohner PI

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So, can I just simply copy that to MAX where I marked? If I will put vol pot to stock place and from there to this PI, does that 300k resistor have to be there or do I have to add some components or change values? PPIMV-pot, how I do that, using stereo pot. from the anodes after 22nF caps to left legs, right legs to ground and middle legs to where it originally goes after 22nF caps, or how? Voltages then, 320V-360V PI anodes vs. ground? How I do regulate that, do I change anode resistor values or put resistor before them or? And entry stage 240V-260V, what's that and how do I regulate it? Sorry 'bout stupid questions, feeling little like this :think_1: :nutjob: :dumass:
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Re: MAX Forty "Devil"

Postby Racing on Sun Feb 14, 2016 10:55 pm

That 300k resistor is just a stopper and seing the amplification factor of the EF-86 upstream..yeah well.
No matter.
No. You don´t need it.

That aside,yes. You can basically just rip-off what´s in that schem. Piece by piece.
The 62k negative feedback line tho...just omit that for now. Stock the MAX amp has a winding of its own for that on the OT (a couple of white wires)..just fold that back.

That said. Yeah. In essence you got the majors of it. A PPIMV pot in turn is as i´ve explained just a stereopot. Ie;two pots on a common axle. Yes. You decouple that pot completely. Caps inbound and caps outbound. Correct. The trick with PPIMV´s is to regard the load they present the PI. There´s no such thing as a setup that wins all the marbles but..we can get close. For starters though,not to cluster this up for you,simply install a 2*500k log pot. From the rear of the pot the two legs to the left are folded together and soldered,from there a wire vs ground. The right pair of solderprongs need to be adressed as individuals. One for each side of the PI. Ditto for the center/wiper lugs. These are what´s headed for the powertubes control grids.
Be aware that the negative bias voltage needs to be presented at the correct pair of caps..and correct side of these.

As plate resistor value is more or less set we alter a triodes behavior by altering the rail voltage ahead of it. Rail voltage is normally set by drop resistors. Ie;to get a certain rail voltage you simply use different resistor values. That simple.
Empiric testing will tell the story.
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Re: MAX Forty "Devil"

Postby Antti M. on Mon Feb 15, 2016 6:44 pm

Tried to draw again, picture explains better...few terms little unclear to me like Rail voltage and entry stage, tried to google, but didn't help much so I tried to use common sense and guess... :roll:

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EDIT: updated scetch
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Re: MAX Forty "Devil"

Postby Racing on Wed May 25, 2016 1:03 am

Maybe a bit of an explanation is in order.
Antti found me on FB and..we kind of took it from there.

That is not to say that the MAX amp saga has come to an end tho! Not by a friggin longshot even! Read on.. :mrgreen:

As that No1 got stolen i struck gold and found No2 alright,which you can read about a few pages back. No2 is since up and running,albeit i still need to toss a few tweaks at it to come full circle for my taste.
Now..a backup is always nice when you go live right and..this add popped up on our local CL. Another MAX Forty for sale like a 150 clicks north of here,in other words a 300km roundtrip.

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Amp was complete alright,just lacked the wooden plate out back,which the thieves that stole No1 left behind...so no harm no foul from that perspective.

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Yep. All there. Tfk powertubes out back and all. Handed it a check over and fired her up and sure enough. We had sound. Of a stocker,which is out. But....the amp worked at least.

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Yeah well. As half assed isn´t exactly my middle name,go figure. Basically i cleaned this puppy out totally. For the better,and seing what that involved i believe i´ll to a degree redo No2 as well as time permits.
Now..
That COULD have been the end of the saga right? Got me a No2 and a No3..all good.
No.

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Friend "Chopper" called me up and told me he had grown tired of his stock MAX Forty "bass"! Didn´t even know one existed! Well..proof is right there in the puddin´...
So. We did a trade,which in effect made me end up with No4. Thus far i haven´t really dug into it but..

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Chopper had already replaced the stock main e-lytes and the top hats for the powertubes. In turn the actual powertubes were basically brand new RFT ones. Cool!

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Again..all stock. Well,they have been replaced alright but the actual layout is as stock as it comes.

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Powertube sockets..stock. Have to say that the right gridstopper looks a little suspect tho.

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Uhu. Stock mains switch and in turn just as stock "death cap".

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As clean as the stock tagboard is,as clustered to the looks is the rear of the pots. A bit like old Vox amps actually when you think of it...
Difference,for this "bass" model is within the tonecontrols. It uses somewhat different capacitor values mainly.

So.
What gives? What´s the plan?
As they became three...i honestly don´t know as of this writing. Nor am i in any kind of hurry to figure it out TBH...we´ll get there..
As is i find it kind of neat to own three of them. Thieves be damned.
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Re: MAX Forty "Devil"

Postby Racing on Wed May 25, 2016 8:00 pm

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Uhu. For once a few moments on one of my own amps.. 8) . Individually adjustable bias a complete preamp and in turn what´s needed to run the PI. All of the caps are located underneath the board.
Main reason for the dual bias pots is that these amps use EL-36 powertubes,and it´s uncommon that these are found in matched pairs.
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