Putting together a Mark III Guide

[jrb32]

Just to sum up this entire thread at the start to save you reading through:

Black/No Stripe or Black Dot - Essentially the original schematic based off the incorrect IIC+ schematic with R130 and R126 for R2 channel. C214 added in later for R2 channel on transition models between late 85 and early 86. There was a PCB board change to do this.
Purple - A late black stripe with basically a IIC+ lead circuit minus a few slight component value changes. But then C26 removed to make it less like a IIC+ in the EQ section... VERY underlooked amp. Easiest to + mod in my opinion. Great tones from it too and gain (this is NOT a low gain amp despite the rumours).
Red - A purple stripe but some weird preamp values going on. Lead circuit now almost identical to IIC+. R2 channel changed to remove R126. In its place sticks in an automatic treble shift to be enabled when in R2 mode via an additional LDR. This supposedly causes humming issues and you need to turn treble shift off to get it to sound more like a IIC+ in lead mode.
Blue - 2.2M for R106. Crazy gain lead channel that was completely overhauled. Same R2 channel as Red. Power section finally has 0.0047uF presence cap and 1.5K presence control resistor (same as IIC+)
Green - same as a blue but has 3.3M for R106. Outer simul power valves wired in pentode.

There was a Reverb mod/fix done at the factory. If this was done there will be a big R written on the back. This essentially adds a 120K 2W resistor from R116 to ground and also a 1K or 3.3K resistor on the SEND/RETURN black lead. I'm not 100% sure on the reason for this but it's supposed to sort an issue with the reverb distorting or causing interference. Personally I have also found you can get a popping noise on the speaker sometimes causing interference without this 120K resistor in place. The fix hasn't got anything to do with increasing reverb strength and, in my experience, it does change the overall tone of the amp and I wasn't a fan so removed it. The 1K/3.3K is worth keeping though for definite. This was a Reverb mod done on the IIC+.
Some people say you can sort this reverb issue by moving the reverb tank around 180 degrees so the reverb tank plugs are no longer under the power transformer. I had some success with this.
I ended up removing this 120K resistor and made the voltage rail going to R116 from C to B on the schematics. I did this with running wire off the B rail 30uF cap to R116 with one leg of R116 lifted off the board going to this wire and this got rid of the popping or distorting issue and for all and made the reverb all so sweet (make sure you secure it properly – glue gun etc.). This B rail is how it's done in the C+. I'd recommend upping R116 to a 2W resistor though in this scenario definitely.

The Mike B III+ mod is something I have documented but would rather not reveal. Like the IIC to IIC+ upgrade steps I don’t want idiots going and ruining their amps. The whole point of me doing this is so competent people might be able to fix other people’s screw ups! Basically, always send stuff to Mike B at the Mesa factory if you’re in the USA! If you’re unable like me living too far away all I can say is that it mods a III to how you would think it would be done – lead section and EQ section have major changes, especially the EQ section. Power section remains basically the same with minor changes. Again, the Preamp section only has minor changes.
Regarding the cathode for the preamp in general - if your amp has 22K and the schematic says 15K relax or 22uF vs 20uF vs 15uF – relax. Those values seem to be used interchangeable. Plus if you’re expecting one schematic for a IIC+ to be exact with no random component values every so often think again!

NO STRIPE/BLACK STRIPE/DOT CP1D LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1yG8gKaNOHx-Otu3nKAQacFCvo5cu0CK2
BOARD VIEW: https://drive.google.com/open?id=1boo0UX7jW7Rk9KUzPnLwNO1mIyigNuog
TINYCAD FILE: https://drive.google.com/open?id=1ATlQrZew2GiDMvKitlR7HXeAVviBnAU4

NO STRIPE/BLACK STRIPE/DOT CP1E LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1fAjkr2xCf3IyR-wjkaTMNRrhnay8ZXjJ
BOARD VIEW: https://drive.google.com/open?id=1vurMaY128ZuHSnB3kQGgo8kTfTuyGAuH
TINYCAD FILE: https://drive.google.com/open?id=1WQjZ_YSHlF4ivqUo21gaGlbWj3TG7F9r

PURPLE STRIPE CP1F LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1QRuyCBLnwRUqao6atsabvFMqApbrxWXv
BOARD VIEW: https://drive.google.com/open?id=14wHkaoqae6PFQn5RFZwDwxJz0HFRDXON
TINYCAD FILE: https://drive.google.com/open?id=1-0lSsEbqHNKIVU2BdvvETvv34OuzKMMo

RED STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1o965ZpLjc7Oc5weWOS8stDsDycfzlBJX
BOARD VIEW: https://drive.google.com/open?id=1kf7xBblJ6qY1ZdxjI8Ek6hC1fO-vkEAO
TINYCAD FILE: https://drive.google.com/open?id=1hVEeG7mbBdaBq_t8SHqzmM4A3AkPH6l0

BLUE STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1xnKpohT0SYL2LXgNyP_rJCrckxwbt8oJ
BOARD VIEW: https://drive.google.com/open?id=1Mv0qNPZqUyb8JdRSNYHcKhdVgBiBVUhw
TINYCAD FILE: https://drive.google.com/open?id=1y8kdsASPykd5HCbj5aMtqXWfUlITuv0t

GREEN STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=146K06hA7dmAJzgq9RZ1v1J_5CU9_hXlV
BOARD VIEW: https://drive.google.com/open?id=1MmBK-g9ChqGYKBJHhGSdMOidtRplSIIl
TINYCAD FILE: https://drive.google.com/open?id=12VF0_ulOegnbB3xamCtO8PTKhDVBG1VT


ORIGINAL POST:

Hello! So a lot of stuff has been posted on here about the Mark IIC+ and there is the excellent guide for dummies, however there is not too much info on the Mark III.

I really want to get a guide up but I'm missing some info on component values used in the different stripe values. I have most of the info I need, schematics ready to go and board layouts for these components but ideally some board photos or gut shots would be great of any of the following:

Black Dot/Stripe
Purple Stripe
Red Stripe
Blue Stripe
Green Stripe

The 100% concrete info I have is from my Early 86 where there was a transition period between the Black and Purples using the CP1E board. I'd like to do one for all the Mark IIIs and get a full guide up and running along with general maintenance info. Even better if you don't mind going through your amp using my board view and schematic as a guide and checking the component values that'd be amazing!

I should also be putting up a III+/++ mod guide for each stripe if I can get the info needed for each. HOWEVER, please note the IIIs are great amps and shouldn't be overlooked as being massively inferior to the IIC+. Originally they were designed to be a IIC+ with switchable ++ (the R2 channel) but they went beyond that into new territory with them. Whether this was good or bad is for debate but it happened - deal with it. The other big change is the IIIs use a simplified single PCB board instead of the many individual PCBs used in the IIC+. In developing this amp into a single PCB, Mesa missed a few components though compared to the IIC+. The early IIIs are identical to the official III schematic which was based off the official IIC+ schematic, which is incorrect in a lot of places.

Any info you could contribute would be great! Please don't post full serial numbers but thing like 178XX are cool along with the stripe and amp dates (the bit in sharpie on the chassis) would be amazing!

Many thanks in advance.

 

[stephen sawall]

I had a Mark III red strip I bought new about 1987. It was one of the best amps I have owned. Really looking forward to seeing all of this.

 

[Agustín Collia]

Really looking forward to seeing this finished! I've been following all your posts since you first started posting here, you've done a remarkable job! I've got a 1993 Blue Stripe (which actually hasn't got a stripe on it, I just know it's a Blue Stripe because it's a 100/60 model, and all Green Stripes were Simul Class). It's factory wired to 230v, which adds to its' awkwardness. I's love to post the gut shots here, but I don't know how to post pictures!

 

[modder]

IIRC There were a few Greens wired 100/60w.

 

[jrb32]

Really looking forward to seeing this finished! I've been following all your posts since you first started posting here, you've done a remarkable job! I've got a 1993 Blue Stripe (which actually hasn't got a stripe on it, I just know it's a Blue Stripe because it's a 100/60 model, and all Green Stripes were Simul Class). It's factory wired to 230v, which adds to its' awkwardness. I's love to post the gut shots here, but I don't know how to post pictures!

Cheers! A lot to do still but I'm getting there. For gut shots https://imgbb.com/ is pretty good. If not PM me and I'll give you my email address

Any help would be great thanks!!

Jon

 

[Fleflo]

This is just great!
I´m looking forward to see this.

 

[jrb32]

OK may as well start from the top! Any errors please let me know.

BLACK STRIPE/DOT CP1D LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1yG8gKaNOHx-Otu3nKAQacFCvo5cu0CK2
BOARD VIEW: https://drive.google.com/open?id=1boo0UX7jW7Rk9KUzPnLwNO1mIyigNuog
TINYCAD FILE: https://drive.google.com/open?id=1ATlQrZew2GiDMvKitlR7HXeAVviBnAU4

 

[jrb32]

BLACK STRIPE/DOT CP1E LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1fAjkr2xCf3IyR-wjkaTMNRrhnay8ZXjJ
BOARD VIEW: https://drive.google.com/open?id=1vurMaY128ZuHSnB3kQGgo8kTfTuyGAuH
TINYCAD FILE: https://drive.google.com/open?id=1WQjZ_YSHlF4ivqUo21gaGlbWj3TG7F9r

 

[jrb32]

I need some photos of a Purple Stripe though (I have one grainy rubbish shot so far...), a Red Stripe (mainly the power section and the orange drop and ceramic capacitor values) and a blue stripe (again the power section and the orange drop and ceramic capacitor values). Everything else I've pretty much got concrete info on and the Green I have a complete schematic of thanks to lions letting me upgrade his! Any photos of info you have give me a shout!

Interestingly from the values for a Purple Stripe I've been told, the Purple Stripe is actually really close to a IIC+ and actually has essentially the same lead section as a Red Stripe. It's much much closer to the IIC+ than the Black Stripes which is curious as it gets a reputation for being a mellow and calm amp...

 

[lovetoboogie]

I admire your work...

I have many Mark III's reaching the bench. Here is a stock Red Stripe Simul (sharpied 4/87) if you need any additional photos , etc...lemme know while I have it open. Came in for a broken EQ assign switch and while I had it open the B+ caps and low voltage rail current resistor got replaced....otherwise it's amazing how this thing has held up.

 

[jrb32]

Amazing thanks!! Can I check the board is a CP1F (should say near the lower bottom right 30uF filter cap). Thanks!

 

[lovetoboogie]

It's CP1G ©1984

 

[jrb32]

It's CP1G ©1984

Ooo curious. That means they stuck with the CP1G board from the Red Stripe onwards to the Green Stripe.

Also that Red Stripe was wired by Kaydee - that's one lucky amp owner! The neatest wirer out there of the IIC+/III era

 

[jrb32]

PURPLE STRIPE CP1F LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1QRuyCBLnwRUqao6atsabvFMqApbrxWXv
BOARD VIEW: https://drive.google.com/open?id=14wHkaoqae6PFQn5RFZwDwxJz0HFRDXON
TINYCAD FILE: https://drive.google.com/open?id=1-0lSsEbqHNKIVU2BdvvETvv34OuzKMMo

 

[jrb32]

RED STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1o965ZpLjc7Oc5weWOS8stDsDycfzlBJX
BOARD VIEW: https://drive.google.com/open?id=1kf7xBblJ6qY1ZdxjI8Ek6hC1fO-vkEAO
TINYCAD FILE: https://drive.google.com/open?id=1hVEeG7mbBdaBq_t8SHqzmM4A3AkPH6l0

 

[jrb32]

BLUE STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=1xnKpohT0SYL2LXgNyP_rJCrckxwbt8oJ
BOARD VIEW: https://drive.google.com/open?id=1Mv0qNPZqUyb8JdRSNYHcKhdVgBiBVUhw
TINYCAD FILE: https://drive.google.com/open?id=1y8kdsASPykd5HCbj5aMtqXWfUlITuv0t

 

[jrb32]

GREEN STRIPE CP1G LAYOUT AND SCHEMATIC:

SCHEMATIC: https://drive.google.com/open?id=146K06hA7dmAJzgq9RZ1v1J_5CU9_hXlV
BOARD VIEW: https://drive.google.com/open?id=1MmBK-g9ChqGYKBJHhGSdMOidtRplSIIl
TINYCAD FILE: https://drive.google.com/open?id=12VF0_ulOegnbB3xamCtO8PTKhDVBG1VT

 

[jrb32]

I've probably made a few errors as some component values I've made an educated guess on, especially the 1KV disc caps, but should pretty much be complete otherwise

Hope that helps someone out there!

Jon

 

[JD]

Great Work Jon

 

[Fleflo]

Superb!