Mark III to Mark II mod

[The Last Jedi]

Hello,

I'm searching the last few months to make a mod to my mark III purple stripe. Specifically I'd like to mod my purple stripe to a mark II c+. Any ideas of what I have to change in my amp?

Thanks!!!!

 

[jediguitarist]

One of the guys on the forum drew up a IIC+ schematic

http://forum.grailtone.com/viewtopic.php?f=27&t=74680

You could find a Mark III schematic and compare the two.

 

[The Last Jedi]

Thanks for the info!!!
I was wondering if anyone had modified the amp in the past so he could share some info on what i have to do exactly.

 

[darkbluemurder]

Here is what I did to my purple stripe:

1. Change C30 from 0.002uf to 0.001uf.
2. Change C516 from 0.01uf to 0.0047uf (this cap is in the feedback circuit in the output section)

Check whether the output of the lead circuit has the 220k II 250pf to 100k II 500pf voltage divider. My amp had it but the Mesa Mk III schematic does not have it.

I would not bother changing the 470k to ground (coming from the 3.3M series resistor) to 680k, unless you want exact IIC+ spec. You will lose clean headroom, and it will not make a noticeable difference in the lead mode because it is parallel to the 100k resistor to ground that is part of the voltage divider (see before).

Cheers Stephan

 

[The Last Jedi]

OK thanks a lot for the info!!!
I'll do it and be back with the result!!
Thanks!!!

 

[gts]

Hello,

I'm searching the last few months to make a mod to my mark III purple stripe. Specifically I'd like to mod my purple stripe to a mark II c+. Any ideas of what I have to change in my amp?

Thanks!!!!

Can't be done.
Most notably because the IIC(+) and Mk-III have different pre-amp circuit boards.
Never mind the PT etc....

 

[darkbluemurder]

Can't be done.
Most notably because the IIC(+) and Mk-III have different pre-amp circuit boards.
Never mind the PT etc....

I guess you meant by "can't be done" "can't be done exactly", and if so, I agree. Different circuit boards have different stray capacitances.

I also agree that power transformers have an influence on the tone, and it is well known that the transformers on the Mark IIC+ were different. But the mods suggested will get the purple stripe in the ballpark. This may be all the OP wants/needs.

Cheers Stephan

 

[gts]

Can't be done.
Most notably because the IIC(+) and Mk-III have different pre-amp circuit boards.
Never mind the PT etc....

I guess you meant by "can't be done" "can't be done exactly", and if so, I agree. Different circuit boards have different stray capacitances.

I also agree that power transformers have an influence on the tone, and it is well known that the transformers on the Mark IIC+ were different. But the mods suggested will get the purple stripe in the ballpark. This may be all the OP wants/needs.

Cheers Stephan

Perhaps but he didn't ask for "ballpark" he stated "Specifically I'd like to mod my purple stripe to a mark II c+"
Which is why I posted it can't be done.
And even a "ballpark" mod doesn't come close. The way a C+ responds to your playing is very different than any MkIII will ever respond be it modded or otherwise.

Fwiw a lot of folks out there are misinformed about what Mark series amps can be modified to a C+ and which can't (and why).
Best to give him accurate info and not continue to perpetuate the mis-perceptions/ misinformation out there....

 

[darkbluemurder]

Fwiw a lot of folks out there are misinformed about what Mark series amps can be modified to a C+ and which can't (and why).

From what I have read the IICs can be upgraded to a IIC+, which is what MB have offered as a factory upgrade. I also know that the first Mark IIIs (no stripe/dot/black stripe) had the same power transformers so they would be the next best candidates. Everything else is too different to be modded to be "exact IIC+". Please feel free to confirm or correct.

Cheers Stephan

 

[s-fresh]

For a long time there were spare preamp boards to be used in these projects, but they have run out so now it's basically just IICs that can be upgraded.

 

[Wyzard]

The best MkIIIs - I've had almost all the flavours, from Black Dot to Green - can get close-ish to MkIIC+, but are better viewed as great amps in their own right. They're good value, and are amenable to improving mods in both circuit and tube complement. The Black Dot Export is my own current favourite, having had a thing for Blue Stripes for some time. But it's still not a IIC+.

Since the boards necessary for conversion are exhausted, gts' comments are fair IMO. If you want a IIC/IIC+ then start searching, and be prepared to pay up. The reason for their perceived value isn't the recorded sound that we've all heard - it's the feel of the amp, in the room, that makes you play a certain way, which in turn leads to the great sound we've all heard on record/live.

Incidentally, the II series Marks (of all kinds) breathe differently from IIIs, as well as from each other; yet I'd still say I can get closer with my favourite Coli IIB than with any III, albeit boosted and at some considerable volume....!

If you have - or want - a great MkIII, they're cheap enough to buy and sell a few times in succession, in search of the one that best fits your playing. They're fine amps, hold up well once properly serviced, and are still under-valued enough to allow you to spend a bit more on good tubes (to sub in until you find your preferred gain structure).

 

[xdg999]

I tried a Mark lll+ red stripe and a Studio Preamp side by side a couple of years ago. The Studio Pre was closer to the feel of a c+ than the lll+. There are deals out there. I got the wide chassis factory c+ for $1660. I paid $1595 for the llc DRG and road case + about $700 for the c+ upgrade, new caps and shipping. There is a difference between the 100 and 105 transformers and between the HR's and Simul's but I'd be happy owning any version of the c+.

 

[modder]

I tried a Mark lll+ red stripe and a Studio Preamp side by side a couple of years ago. The Studio Pre was closer to the feel of a c+ than the lll+. There are deals out there. I got the wide chassis factory c+ for $1660. I paid $1595 for the llc DRG and road case + about $700 for the c+ upgrade, new caps and shipping. There is a difference between the 100 and 105 transformers and between the HR's and Simul's but I'd be happy owning any version of the c+.

What was the pre through?

 

[xdg999]

The Studio Pre was run through an old Zenith 6V6 stereo amp that was converted to a guitar amp.

 

[jrb32]

I’m pretty sure you could modify the preamp of a III to a IIC+ without much problem and get 95% close to a IIC+ easily enough. They’re not some mythical creature that have a hidden mystery component inside and some are definitely better (and worse!) than others in that they vary a lot in resistor and cap type. They also vary a lot in values and different components if they were an original factory C+ or an upgraded C. It will take some minor PCB mods on a III to do this, at the least disconnecting some components and maybe running wires to other bits of the board but it's definitely possible! I’m planning on doing this though to my recently aquired III Early Black Stripe and will report back. I would imagine the reason the III+ mod doesn’t replicate this turning the III into a clone of the IIC+ preamp because the III+ mod is more simple component value changes or cap additions rather than any PCB mods which would be time consuming and costly for Mesa.

For as close a conversion as possible, the more difficult bit to sort is the output transformer and the power voltage rails which are different on the III vs IIC+. If you have an early Black Stripe III with the IIC+ transformer I don’t see this as impossible though. You’d need to add a filter cap and mod the PCB slightly for the different voltage rails but it’s certainly achievable.

It wouldn’t be a ‘verified’ IIC+ but would be near enough identical. I’ll try it out and see what happens give me a few weeks though with work commitments at the moment though.

Jon

 

[gts]

I’m pretty sure you could modify the preamp of a III to a IIC+ without much problem and get 95% close to a IIC+ easily enough. They’re not some mythical creature that have a hidden mystery component inside and some are definitely better (and worse!) than others in that they vary a lot in resistor and cap type. They also vary a lot in values and different components if they were an original factory C+ or an upgraded C. It will take some minor PCB mods on a III to do this, at the least disconnecting some components and maybe running wires to other bits of the board but it's definitely possible! I’m planning on doing this though to my recently aquired III Early Black Stripe and will report back. I would imagine the reason the III+ mod doesn’t replicate this turning the III into a clone of the IIC+ preamp because the III+ mod is more simple component value changes or cap additions rather than any PCB mods which would be time consuming and costly for Mesa.

For as close a conversion as possible, the more difficult bit to sort is the output transformer and the power voltage rails which are different on the III vs IIC+. If you have an early Black Stripe III with the IIC+ transformer I don’t see this as impossible though. You’d need to add a filter cap and mod the PCB slightly for the different voltage rails but it’s certainly achievable.

It wouldn’t be a ‘verified’ IIC+ but would be near enough identical. I’ll try it out and see what happens give me a few weeks though with work commitments at the moment though.

Jon

Oh God here we go again.... :roll:
Jon your intentions might be noble but seriously if it was as simple (or "minor") as you describe it'd have already been done.

 

[jrb32]

Oh God here we go again....
Jon your intentions might be noble but seriously if it was as simple (or "minor") as you describe it'd have already been done.

I know I know! But hear me out. Are we at least in agreement that the Red Stripe is at least similar in sound to the IIC+ but not the right 'feel'? The preamp section of the Red Stripe is almost identical to the IIC+ apart from:

R226
R223
R105
C506

Which have different values. Change these (simple component changes with no PCB mods) and you have exactly the same preamp as a IIC+, but it still isn't 'right'. I agree,
However, imagine you could put this preamp through a IIC+ power amp? It would be pretty much there in my opinion. Add the additional voltage rail for some of the preamp valves and it would be identical.

This is EXACTLY what you would be doing if you modded an early Black Stripe to Red Stripe specs, then changed R226, R223, R105, C506, added the additional voltage rail and changed the C516 presence cap to 5000pF. The only difference is the slightly different tolerances of having a different PCB layout in the IIC+, and the V3 and V4 valves being separate.

If you wanted to go a lot further you could make up a PCB clone of the IIC+ and swap the components over, but obviously that's crazy advanced for most people.

My point is that when you say it is 'impossible' it's not. You just need the right amp to begin with. So modding a purple stripe and later stripes to IIC+ specs can definitely be done, but it will never have the right feel unless you get hold of some IIC+ transformers. That I’ll definitely agree with you on.

Thanks,

Jon

 

[Wyzard]

Given that my two IIC+s sound and respond differently enough to reliably tell them apart blindfold; and given that everyone else's various IIC+s all sound different from each other in a variety of ways.... and given that we all like different things about these amps anyway; and further given that a modded amp is an uncertain proposition versus a known outcome:

if you picked a great sounding MkIII (presumably you wouldn't start with a bad-sounding one - that'd be a recipe for yet more uncertainty before you even began), and modded it to get to some approximation of a MkIIC+.... you might end up losing something that is really good in its own right. Trey's red stripe sounded pretty good (on the half-power setting I think) on a lot of live material IMO. Not to mention that MkIII Colis are among my favourite of all the Marks, and I think that modding a good one of those would constitute an actual crime!

All to gain something that, try as you might, will never actually become a IIC+.

 

[jrb32]

if you picked a great sounding MkIII (presumably you wouldn't start with a bad-sounding one - that'd be a recipe for yet more uncertainty before you even began), and modded it to get to some approximation of a MkIIC+.... you might end up losing something that is really good in its own right. Trey's red stripe sounded pretty good (on the half-power setting I think) on a lot of live material IMO. Not to mention that MkIII Colis are among my favourite of all the Marks, and I think that modding a good one of those would constitute an actual crime!

Definitely agree! Just because you can do something doesn't mean you should!!! There's no substitute for having a great amp or sound you like to begin with, so if you don't like the feel/sound of your III look at getting a different amp! So yes it is possible to mod a III to a IIC+ but DON'T unless you really know what you're doing and are seeing it more as an experiment than a 100% reliable result. As stated before if you don't like the sound of your III then this will not transform it into something amazing, just shape the sound slightly, maybe for better maybe for worse!

That said, if you want to experiment change components one at a time and always keep the originals secure, labelled and make a note of where they go! But the main things to change to shape a III to a IIC+ (for a black/no stripe) would be:

C506 change from 0.047uF to 0.1uF
C502 change from 0.047uF to 0.022uF
Replace 150K resistor from V3A Grid to Cathode with 470K
Add 120pF 1KV ceramic disc or mica between V3A Grid and Cathode
Change C30 from 2000pf to 1000pf 1Kv ceramic disc or mica
C215 replace .22 cap with .22 Kemet T110 or equivalent military spec
C516 replace 0.01uF (10000pf) presence cap with 0.005 (5000pf). Closest you can get is a 0.0047uF cap

The other component differences between the two are minor I would say but can be done.

Also make a note that the IIC+s use 715ps and 225p capacitors, plus carbon and metal film resistors in random arrangements which I think is one of the reasons for the huge differences you get between different IIC+s. Others have left over components from a IIC to IIC+ conversion and differ as well!

All III stripes vary as well! Trace your own stripe version yourself, compare to the IIC+ schematic I put up (check earlier post where someone linked to it) and know exactly what you're doing first before continuing! As mentioned the Red Stripe is basically a IIC+ preamp already and still doesn't feel like a IIC+, so this is what you can expect if you modify a Purple or Later I would think. The early Black Stripes with the same transformers would get you there but are rarer and are a great amp in their own right. Anything more, as mentioned, you'll be looking at sourcing IIC+ transformers from a IIB and then we get into the butchering amp territory! So if you love your III sound great! If not, sell it and get another one until you do, or get a different amp if the sound is not what you're expecting

Given that my two IIC+s sound and respond differently enough to reliably tell them apart blindfold; and given that everyone else's various IIC+s all sound different from each other in a variety of ways....

Saying that are there any IIC+s out there that people don't really like? Just curious as they differ so much!

 

[xdg999]

I like the 6 that I own. I just don’t get to spend enough time with them.