Mark III to Mark II mod

[xdg999]

I bought a really clean Mark lll black stripe wide head online this morning. Don’t know if it’s a DRG or HRG yet. It has an x under the power cord, 1/2 power switch on the front, x101 transformer, and a quad of 415’s. I plan on keeping it stock for now.

 

[jrb32]

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

I'll happily take some off your hands!! Here the UK it's hard to even find one IIC+ let alone six!

I bought a really clean Mark lll black stripe wide head online this morning. Don’t know if it’s a DRG or HRG yet. It has an x under the power cord, 1/2 power switch on the front, x101 transformer, and a quad of 415’s. I plan on keeping it stock for now.

Fantastic! Let me know how you find it in comparison to other IIIs and your IIC+s out of interest.

 

[modder]

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

I'll happily take some off your hands!! Here the UK it's hard to even find one IIC+ let alone six!

Seconded :lol:

 

[xdg999]

My c+'s ain't goin' nowhere! I didn't plan on owning 6 of them. I just can't resist buying one for a good price. The Mark lll I bought was the same kind of thing. I found it online at a Music Go Round and my curiosity got the best of me. I'll post a review of the Mark lll later today after work.

 

[xdg999]

I'm glad I bought the Mark lll. It's an awesome amp. I like it as much as my c+’s. I’ve already talked to Mike B. about modding it to a lll+. Does it sound and feel like a c+? I think it’s about as close as you can get. It has the elastic, bouncy feel of a c+. It’s not as smooth but I’m hoping the lll+ mod will take care of that. I think it had been sitting idle for a long time. The more I use it, the better it sounds. I can’t wait to hear what it will sound like after Mike B. gets done with it. The 2 c+’s he upgraded for me sound fantastic. I’ll be shipping it back to Mesa in a week or two. I’ll post an update as soon as I get it back.

 

[jrb32]

I'm glad I bought the Mark lll. It's an awesome amp. I like it as much as my c+’s. I’ve already talked to Mike B. about modding it to a lll+. Does it sound and feel like a c+? I think it’s about as close as you can get. It has the elastic, bouncy feel of a c+. It’s not as smooth but I’m hoping the lll+ mod will take care of that. I think it had been sitting idle for a long time. The more I use it, the better it sounds. I can’t wait to hear what it will sound like after Mike B. gets done with it. The 2 c+’s he upgraded for me sound fantastic. I’ll be shipping it back to Mesa in a week or two. I’ll post an update as soon as I get it back.

Tell me about it the early black stripes are great!! Really overlooked amp. Let us know how the III+ mod sounds once Mike B does his magic. One day I hope to own a similar collection but for the moment I'm very jealous!!

In theory the III+ mod on a black stripe with the X101 transformer would basically turn it into a IIC+ with an R2 section which is how the amp was initially intended I think? Unless there's something else hidden which we're missing to the mystery! I'd also recommend the R2 volume mod done while it's there - really helps with channel switching and levels Anyway let us know would be very interested to find out how it sounds.

 

[xdg999]

Mike B. said he automatically does the R2 mod. I asked him what the x under the power cord meant. He said the amp was built right before the Purple Stripe. I won’t argue with anyone but to me this amp is already a c+. It’s the first amp besides a c+ that passes my half hour test. It makes me want to keep playing longer than a half hour. It’s different than my c+’s but not in a bad way. Just like the difference between a Simul and a 100 watt or a 105 and a 100 transformer. As for my collection, I ain’t done yet!

 

[Wyzard]

I sold all my MkIII blue stripes, as I mentioned a while back, and bought an X101 black X/dot instead.

I still prefer my IIC+s, but it's undeniably a really great amp, and one that can be got for very reasonable money.

 

[xdg999]

I finally got around to calling Mesa today to get an RA# for the Mark lll. I had been going back and forth about keeping it stock or modding it. It just sounds so good as is. I can get really good British tones with the current Mesa 12ax7’s and EL34’s in class A. If I load it with nos Chinese military 12ax7’s and Sovtek 5881’s, probably my favorite tube combination, it gets really close to my simul c+’s. Ultimately my curiousty got the best of me and with the R2 mod this is probably as close as I can get to a 3 channel c+. With shipping and shop time I’m guessing it’s going to be 4 to 6 weeks before I get the Mark lll back.

 

[jrb32]

Ultimately my curiousty got the best of me and with the R2 mod this is probably as close as I can get to a 3 channel c+

It'll be worth it don't worry!! The + mod should mainly apply to the lead channel (R153 changed to 470K - more gain, C502 changed to .022 - less bass, C30 changed to .001 - slightly more treble but this might be left stock at .002) and it's in the best hands possible! Mike B should retain the character of the amp while giving it some extra oomph! So with the R2 channel (did you know this was originally used as a +/++ switch on 12 factory C+s that later developed into the R2 channel on the III) it should be an absolute monster!

Really curious to hear how it will turn out too! Cant wait!

In the meantime I'm almost done with my full III to IIC+ conversion experiment on my black stripe. I'm worried about it changing the character of the amp but I've kept all original components and have a background in electronics repair so it's no hassle to swap back for me 8) I wouldn't worry about this happening to yours as mine is a pretty major overhaul rather than some minor tone and gain shaping.

We've also found that there is a later board change in the IIIs to do with the LDR switching for the treble shift and R2 channel (PCB board change from CP1E to CP1G). We think this starts with the Red Stripe onwards but haven't confirmed for a Purple stripe yet but it seems to very much change the character of the amp and it's not confirmed whether this can be reversed yet or what the function is. If anyone's curious it involves an additional LDR stacked on top of LDR1, an addition of D212 and a 360 Ohm resistor in that area and seems to link the R2 channel to the tone stack via the treble shift pull. It is definitely present from the Red, Blue and Green Stripes but cannot be sure for the Purple Stripe. In theory that would have a CP1F board unless this was omitted and went straight to CP1G in production but will need someone with a Purple Stripe to confirm!

Anyway let us know how you get on! Maybe you'll love it so much you'll sell me one of your C+s :lol:

 

[xdg999]

Finally dropped off the Mark lll at the UPS store. $142 to ship it from Chicago. Should get there next Friday. I guess I’ll just have to use one of my c+’s until I get it back.

 

[jrb32]

So I finished off my Mark III Black Stripe to IIC+ conversion over the weekend

I left R201 at 1.5K for increased gain and haven’t done any of the reverb mods yet. I’ve also left R126 as it was to increase gain on the tone stack when the R2 channel is pulled by lifting the ground slightly on the tone stack. This is mainly because it’s so hard to get to. I also left R106 at 3.3M instead of 2.2M (2.2M will increase gain even more) because I feel I definitely do NOT need any more gain after doing all the other stuff!

I used Silver Micas on the 1KV disc capacitors I replaced including the two tone stack ones. Yellow bullet 2.2uF cap on the lead section.

Other minor things I did was replace the 470 Ohm resistors on the Output Valves, R119 because it burns anyway (were lovely black scorch marks under the original!) and R104/R141 for the filter caps with higher W wirewound resistors – I think I used 6W or higher or something stupid, the highest I could get where the resistor was still small enough to fit!

The only difficult section was in the EQ in adding an extra 10uF 63v axial cap and changing the orders of some components, lifting up a couple of the .1uF 400V 715Ps for the EQ section and sticking a component or two in from of them. Elsewhere it was simple component value swaps :

 

[jrb32]

Finally dropped off the Mark lll at the UPS store. $142 to ship it from Chicago. Should get there next Friday. I guess I’ll just have to use one of my c+’s until I get it back.

Looking forward to how it sounds!! I dread to think how much overseas shipping would be from the UK! I'd definitely have to send just the chassis not the whole amp if I ever needed anything done (I've got my eye on an SRG IIC Export at the moment but would need to send to Mike B to do his + magic...)

 

[xdg999]

Good to hear you’re happy with how the Mark lll conversion turned out. Wish I could check it out. I bought a Mark lll DRG Black Dot combo on Sunday night from a Guitar Center in California. It has Gain Boost instead of Pull Deep on the faceplate. Don’t know if it has the 105 yet. Should get it on Friday.

 

[jrb32]

Good to hear you’re happy with how the Mark lll conversion turned out. Wish I could check it out. I bought a Mark lll DRG Black Dot combo on Sunday night from a Guitar Center in California. It has Gain Boost instead of Pull Deep on the faceplate. Don’t know if it has the 105 yet. Should get it on Friday.

You're a buying machine!! Is it a 15XXX serial? Guessing you're gonna keep it stock?

For reference I have a late 1985 571100 power transformer in mine (the UK version of the 561100 which is apparently the same as the C+ X101) but gives out 485V plate voltage so I'm not complaining!!

It also has the T100-152019 100W output transformer dated 1982.

I'll try and borrow an SM57 off a friend and get some decent audio recording done or do a video at some point. As others have mentioned it's not so much how an amp clinically sounds it's how it feels and responds that's the important bit. I can definitely get that IIC+ sound and definitely has that 'feel' I understand now. It also has none of the mushy treble shift issues that have been reported on the Red stripe and later IIIs if anyone is interested.

Looking forward to hearing what you think of the + mod once it's back! I'd love if you could pm me some pics of the circuit boards on both once they're with you if you ever take the chassis out - really curious as I'm trying to document the circuit board and component changes between the different stripe versions and what Mike B does for the + mod - but no problem if not

 

[xdg999]

The Stripe is #1555x, the Dot 1523x. If I like how the Stripe turns out I’ll send the Dot back to Mesa. I’ll send pics of the boards when I can. I can also send pics of my 1988 Carvin x100a. Maybe you can come with a conversion for it too.

 

[fretout]

That’s great to hear that you’re happy with your results!

I’m not sure if I could add anything to this thread, but I own a Mark III+ Coliseum that shares the same transformers with the Mark IIC+ Coliseums, but it’s a no-stripe (which came out just before the black dots).

As far the sound goes, it’s about as close to a IIC+ as you can get, while not being a IIC+. The only discernable difference between the no-stripe Coliseum and a non-upgraded IIC+ is the Coliseum has this “thicker” sound to it, almost like there’s an extra fundamental note coming through the cab. This could be an attribute of the Coliseums, or could be chalked up to the difference between wattages.

As we as the feel goes, I couldn’t tell any difference between the “bounce” of the Coliseum compared to the IIC+, and the tightness/urgency of the Coliseum was right on par with the IIC+s. Feel-wise, I actually liked the Coliseum better, just because it was still tight, but tonally thicker.

All of this to say that on the Mark series timeline, I think the Coliseums bridge the gap between the IIC+s and the IIIs a little close than the 60/90W Marks. Maybe it has something to do with the transformers, but I’m a little skeptical of this because my Blue Stripe Coliseum is much more brash and angry, and makes the no stripe seem a lot smoother. To get the Coliseums dialed in similar, I’d need to jump the Presence up from 4-ish to around 8 to get it in the ballpark.

YMMV, but I like my III+ as it is, and would recommend checking them out if anyone ever has a chance. They’re in the same family as their 90W brothers, but they’ve got a lot more lower range without sacrificing any of the immediacy or “attack” of the Mark series.

 

[modder]

Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get. What led you to keep R126 out of interest? And hard wiring C47 etc to ground?

 

[jrb32]

Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get

Thanks! Now to concentrate on my playing a bit more...

What led you to keep R126 out of interest? And hard wiring C47 etc to ground?

I kept R126 because it will increase gain slightly when R2 engaged but nothing major. Also it's REALLY hard to get to without removing the relay (something I did to trace the board but I am NOT doing again unless I can find a replacement relay as I needed to use hot air and damaged some traces in the process I had to rebuild).

I hard wired R105/C47 to ground because I wanted that to remain to ground when R2 engaged. This is because I want the R2 channel to engage C214 ON/OFF and nothing else for switchable +/++ to get an extra boost. I experimented with replacing R130 with a trim pot but in the end removed it all together as it was a bit muddy for my liking. Removing it made a massive difference! Now I get a slight boost with R2 pulled which you can really feel on the lead channel, but R2 is no longer a distinct channel, which I don't mind as I never used it anyway.

Are you getting any further with your Blue Stripe to IIC+ conversion? I think it's pretty safe to remove LDR6 and the corresponding diode and resistor - it basically forces treble shift to be on in R2 mode as far as I can tell and can be removed if you don't want this.

Another thing I noticed is that I tried the reverb mod (adding a 110K or 120K 2W resistor from R116 to ground) and although it made the reverb really strong, it made the overall amp a lot muddier and I really didn't like the result. I removed it and BAM back to the sound I loved. I ended up putting R242 around R131 which increased the swell without changing the sound of the amp. I have the reverb on about 3-4 now and any more is a bit overpowering.

Just something to note for anyone reading this (yours is a non reverb model though right so wouldn't apply?)

Cheers,

Jon

 

[modder]

Nice one Jon! You've basically got a IIC+ now, as close as anyone is going to get

Thanks! Now to concentrate on my playing a bit more...

What led you to keep R126 out of interest? And hard wiring C47 etc to ground?

I kept R126 because it will increase gain slightly when R2 engaged but nothing major. Also it's REALLY hard to get to without removing the relay (something I did to trace the board but I am NOT doing again unless I can find a replacement relay as I needed to use hot air and damaged some traces in the process I had to rebuild).

I hard wired R105/C47 to ground because I wanted that to remain to ground when R2 engaged. This is because I want the R2 channel to engage C214 ON/OFF and nothing else for switchable +/++ to get an extra boost. I experimented with replacing R130 with a trim pot but in the end removed it all together as it was a bit muddy for my liking. Removing it made a massive difference! Now I get a slight boost with R2 pulled which you can really feel on the lead channel, but R2 is no longer a distinct channel, which I don't mind as I never used it anyway.

Are you getting any further with your Blue Stripe to IIC+ conversion? I think it's pretty safe to remove LDR6 and the corresponding diode and resistor - it basically forces treble shift to be on in R2 mode as far as I can tell and can be removed if you don't want this.

Another thing I noticed is that I tried the reverb mod (adding a 110K or 120K 2W resistor from R116 to ground) and although it made the reverb really strong, it made the overall amp a lot muddier and I really didn't like the result. I removed it and BAM back to the sound I loved. I ended up putting R242 around R131 which increased the swell without changing the sound of the amp. I have the reverb on about 3-4 now and any more is a bit overpowering.

Just something to note for anyone reading this (yours is a non reverb model though right so wouldn't apply?)

Cheers,

Jon

I can't even see R126 on my board. :lol:

Mine is a non reverb you are correct. It's mostly already finished, the mods I've currently got on it are generally just matching component specs to the IIC+ rather than removing the III circuitry. here's what's left to do on my notes:

R1 ++ V1 deletion
Delete R133
Delete C28

R2 ++ V2 restoration
Delete R130
May require deleting R126 [replace with bus wire]
Delete LDR6 circuit entirely [check if safe/effects]

Miscellaneous
Swap R125 (1K) and R204 (1.5k)
C506 0.047 -> 0.01 [some IIC+ puts this at 0.047, verify effect on voicing]
Hardwire C47 & R105 to ground?

Lead
R224 22k to 15k [will only affect pull bright on the lead master]

EQ [tertiary priority]
R263 1M to 470k
Wire 1M resistor before C504 (use OG R263)
Add 10uF 63V Axial polarised capacitor before C503
Add 10k resistor before C503
Remove 56k resistor around LDR7A

Mods to consider if too dark/mushy/grainy
C27 10pf to 20pf [lets more treble through as per simulclass IIC+ & studio pre]
C30 delete [lets more treble through as per simulclass]
C30 500pf [lets more treble through, less pronounced than omitting entirely]

I'm considering leaving LDR6 in and basically turning my amp into a super red stripe, but I can't help wonder if its affecting the tone anywhere else and as I said in that thread, I really never ever use R2 as it is currently voiced as a separate channel, having it as a switchable ++ would only increase its usefulness. I'm 70/30 towards deleting C30 and swapping C27 for 20pf. The amp as it is has great tone but the attack transients aren't where I want them to be, along with the treble shift weirdness. If I was doing these mods myself I'd remove all the III circuitry first and see how it is then, but I'll likely just get it all done at once.

When I get my amp back in a few weeks I'll put up a full list of what I changed, how I went about it, how I perceived the sound changes etc. Plus some clips, maybe even a video.

How much of an effect would you say the EQ mods have had? I'm not really sure if I need them, unless they affect the voicing of the amp rather than the way the EQ works. How did you go about wiring C47 to ground? Does the stock wiring bypass the C47 circuit in R2 mode?