Mark IIC+ - Guide for Dummies

Mark I's, II's, III's and the almight IV

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Mark IIC+ - Guide for Dummies

Post by Boogiebabies » Fri Oct 19, 2007 8:42 pm

The IIC+ Guide

The Chassis Codes –

SR – Sixty Watt -Reverb
SRG- Sixty Watt- Reverb- Graphic
HR – 100 Watt-Reverb
HRG- 100 Watt- Reverb-Graphic
HRGX- 100 Watt-Reverb-Graphic-Export
DR – Simul-Class - Reverb
DRG- Simul-EQ-Reverb
DRGX- Simul-EQ-Reverb-Export
K - Coliseum / Series 300

You could get a standard 60 or 100 watt with no graphic or reverb so there are possible S, D and H only chassis codes. Any amp could have an export power transformer, so an X is possible as well. For example, SX, DX and HX.

A 15” could be added to the chassis code designating a long chassis.

The Number after chassis code –

This is the week of production.

Example – A DRG 6 is a Simul-EQ-Reverb from production week six.

For Reference – The DRG 6 was finished in 6/84.
Estimated start of production is early to mid April 1984, or about two months prior to final tech date.

The Options –

The cabinet and chassis could be ordered as a standard head, standard 1x12 Combo, 1X15 Combo, 15” Head and all could be
tolex, hardwood, but only combos have the SUS-4 Shock Mount option. They could be ordered with the “Boogie” logo or the “Mesa Boogie” logo. The “Mesa Boogie” logo appeared primarily on the long chassis heads, but you could have requested on an any amp.

A ridiculous option known as the 300 series was also available.
The 180 Watt, Six 6L6 powered behemoth could be ordered with all the classic options and had a half power switch. Almost all had a limiter circuit to reduce the ouput volume of these 180 Boogie watts. From time to time, one can see a Simul-Class 300 150W series running two EL-34’s in the center sockets and four 6L6GC’s in the outer four sockets.

The “+”-

The plus is dedicated to IIC’s after the 12,500 production.
There have been documented +’s as low as 12337, mainly in some prototype, nearly stock or customized circuits. In recent months I have witnessed two IIC I’s. These are IIC’s that almost made it to a plus, but had “Pull Deep” faceplates and a stock IIC circuit with the RP11A circuit board. These were very interesting times at Mesa. A customer could have chosen a C or a C+, hence, the “I” looks like the initial swipe of a +, but never got the other horizontal swipe so do your loop tests. I could imagine Mesa having to call on all outstanding IIC orders and asking if they wanted the upgrade. In the C+ transistion around 12,3XX/124XX
a “yes” meant a plus and a “no” could be the “I”. In my opinion, the earliest orders for a IIC+ were made in late November and December of 1983. The earliest IIC+ found to date was a 12,33X dated 2/84.

A “+” also refers to any amplifier upgraded below 12,500 that has been verified either by the loop test or visual circuit identification. If your amp was upgraded in the early 90’s to the present, Mesa will have an RA, or Return Authorization verifying the upgrade. Mike B. has a very good catalogue of the amps he upgraded, but please call customer service with the serial number first and let the guy earn a living. The amp may have the 100 or the 105 PT. For those seeking originality, the 105 would be the production transformer. In some opinion’s, and depending on playing style the 100 may be a better fit and offers a smoother tone than the 105. It’s really up to personal preference for tone or originality. Now, if Mesa found two 100’s On a shelf in stock room during the C+ production, they would use them, so never put it past Mesa to be frugal. Some also infer that the Export, or X101 is the most suitable transformer for the C+. Again, it is up to your personal preference. Another view of Mesa’s frugal nature is it took half a year to finally get “Pull Deep” face plates for the 15” models. These 15” chassis +’s have been left to doubt, rumor and speculation as to the amps authenticity. A simple serial number should dispel any questions. If it’s above 12,500, 15” wide and sounds awesome, you should not have to question the “Gain Boost” face plate not being a +.

The Quest –

Sometime in late winter 1983 Randall Smith was attending the Musik Messe in Germany to represent Mesa/Boogie products in the European market. During his absence, Mike Bendinelli and Doug West decided to modify the IIC.
A few weeks of R&D turned out to be a significant step in the evolution of the high gain tube amp. Although the original modifications proved to be a move in the right direction, I am sure that the tone obsessed duo would not be satisfied until they nailed it. The final design did not go into production until about February 1984. In essence, the C+ circuit was born sometime in January of 1984. This circuit has the tendency for extreme gain and brightness. When asking Mike B. why the IIC+ was so bright he kindly replied, “That was Doug West, he kept saying make it brighter”. Doug was obviously looking to shred without the assistance of a boost pedal and got what he wanted. The moral of the story is why the cats away the techs will play. Obviously Randall was impressed with the results and gave the green light for the change in circuit design and production. I also must admit that the 100 PT was probably being phased out. Many 105’s date to late 1983. The X101’s could date back to 1982. Another oddity is that Mesa was going to the “Pull Deep” face plates as well. The 1983 Christmas card shows the IIC with a “Pull Deep” face plate. It makes more sense as it adds a minimum of gain and a wall of bottom end. Knowing Mesa’s frugal nature, they probably sat boxed until they ran out of the previous plates.

The rest is history.

The Tech –

Below the power cord are the famous initials MB, for Mike Bendinelli. No, he did not build every amp, he did the vast majority of final inspections and Burn ins. If you look at the circuit boards they have the initials of the person who populated each individual board. If you’re lucky enough to have a final inspection tag, you we get the initials of everyone who built your amp. Any C+ could have the initials MB, PC, SDG, BN, CD, RH, LB, PG and RCS, yes the man himself. Doug West, or DW is most commonly found as the final play tester on the hang tags that came with the amp.

To dispel a myth, Mike B. was not the only person to perform the final Inspection of the IIC+ amps. A very small number of them are signed “RCS”. Yes, that it Randall C. Smith. Who do you think covered for Mike when he had to take an off site tech visit to Prince on the Purple Rain Tour in late 1984? Also, Mike had vacations, but he has mentioned coming back to piles of amps so the initials RCS are pretty much an Alien sighting on the back of the IIC+, but they do exist. I have only found three with Smith's initials.
An 11/84 RCS IIC+ with Simul-EQ and Reverb was sold on E-Bay in April, 2007 and July, 2008.

The Face Plates –

The stock face plate should say “Pull Deep” over the Master volume. If it says “Gain Boost” it is the IIC face plate and you should do the loop test regardless of the “+” marked status if the serial number does not fit the sequence. The exceptions would be a 15” chassis above 12,500. Mesa used the remaining 15” IIC face plates before rotating to the “Pull Deep” stock. Late IIC non-eq amps used the beginning "Pull Deep" plates.

Note: Pull Deep Face Plates Appear in the 1983 Christmas Card.

Long chassis face plates can have a Full PWR / 1/2 PWR switch on the front. The only way to determine what effect the power drop will be is if you know your amp is a 60/100 or Simul-Class. Some C+'s did not come with a Simul-Class sticker. The identity can be found by looking at the output transformer part number. For the 300 Series, it will drop the center two of the six 6L6's for the 180 Watt and 2 outer sockets on Simul-Class models.

The early “Pull Deep” plates had a dark gray EQ face and the EQ toggle order is –

Top – Auto
Middle – Out
Bottom – In

The Later Plates had light gray EQ face, which scratched much easier. The change in toggle order is probably by customer request or a change in the availability of the switch.

The EQ toggle order is –

Top- Auto
Middle - In
Bottom – Out

The EQ face was later changed back to the darker gray face with the same toggle functions.

The Loop Test –

1) Plug your guitar into the Effects Return jack
2) Switch to lead mode
3) Turn the Lead Drive and Gain controls with a note ringing.
4) If they have NO effect on the volume and sound you have a+.

The Circuit Boards –

Preamp – SP11A – Early 60/100 non Reverb.

SP-11A – Simul-60-100 watt non-reverb
RP-11A Simul-100 and 60 Watt Reverb

The SP-11A, RP-10 and RP-11A were designed for the MK IIC. Their use was continued with the IIC+, Hence, the ability to upgrade from IIC to IC+.

Power Amp – PWR- 7-C1 Simul-Class and 100
PWR -7D – 60 watt.

Filter Cap – PS-1C
Coliseum - PS-2C

Limit Circuit - DR-1A
Limit uses a 12AT7 and 6FQ7/6CG7 tube for PI and Limiter.

Upgrade Info:

The RP-10A is based in the style of the IIB with LDR's for switching instead of the one relay. The RP-11A is the circuit board that was
redesigned for the IIC with a much different layout. It was also later the board used in the IIC+ with many component changes and
a different circuit layout. From what I could find out about the RP-10A, it was the early production IIC PCB. It was changed somewhere in the mid range
to the RP-11 in mid to late 1983. Hence, both boards have 1983 copyrights. The reason the RP-10 can be upgraded is the five LDR's. The rest of the
circuit Mike B. just does his magic on.

This info does not pertain to non-reverb models of the IIC or IIC+. The "R" in RP-10 or 11 is for reverb.
The SP-11A would be the pcb for these amps from IIC revision one and two.

The Soup –

The components used in the manufacture of the IIC+ vary widely from start to finish. From resistors to capacitors you will see changes in size, color and type of construction. Some have metal film resistors in certain amps, while others have carbon film. Dale metal film resistors were mostly used on the V1. The coupling caps could be Sprague 715P, 225P, Mallory Orange Drops and all could be used in any section of the preamp. The cathode caps are generally black Mallory’s and in certain areas of the circuit, a military specification hermetically sealed silver cap was most often used on the .22 Pull Bright, Graphic EQ, V1A Pull Shift circuit and the 3.3uf cap for the V4B reverb cathode. Substitutions are common so you may see all of the above replaced with the same value in the black Mallory or even an ITT case. The pot tolerances are all over the map. After July or August of 1984 Mesa had to use a 22K series resistor with the Master Volume pot as CTS switched production from the USA to Taiwan. These early Taiwanese pots would have your Master Volume pumping out the volume of 5 at a setting of 2. From this point on, the series resistor stayed and is still in use on the MK IV today. So if you think all IIC+’s will sound the same, think again. Some will be louder with the Volume 1 and Lead Drive set to 7 and others may need to go to a Master of 3 and Lead Master of 8 or 9. The same is accurate for the EQ settings. One of the most consistent components is the graphic EQ. It’s surprising that when you set them all flat, it basically sounds exactly like having the EQ out. A special debt of gratitude goes to Richard Ray who always told us to use our ears and not the numbers on the knobs.


The dark brown preamp resistors that look like 1/4 watt are 1/2 watt Beyschlag.
After August 1984 the 120pf cap from the grid to the cathode on V2B was removed. This is the effects loop signal, lead master and reverb output
from V2A.

The Schumacher Transformers –

The digits 606 are Schumacher’s EIA manufacturer code.

The digits after are the last number of the production year, example, 3 is 1983. The next two digits are the week of productions, example, 42 is the 42’nd week of 1983. It’s not the Fibonacci Sequence, trust me. EIA 606-342.

60W OT - T60-152019
Simul Output - SC-152019B – Simul-Class
180W - SD 190555 Coliseum

60W PT - 00-162310 - 448V
60W Export - PT: X62-162318 - 448V
Early 100 - 100-162318 - 448V
Simul/60-100 Power - 105-162318 -483V+
- X101-162318 – Export - 448-460V
180W - 0180322 Coliseum - 500V+

Some early IIC+’s may have leftover 100 power transformers.

The Serial Numbers –

12,500 to 14,400 are pretty much unquestionable. 14,400 to 15,000 in my opinion have early black dot MK III’s in the serial number sequence, or were never even used. There has been visual proof that a 15,000 does exist ( BWK aka Ian Dickey), but IIC +’s between 14,400 and 15,000 just never seem to surface. Anything from 12,300 to 12,499 is a certain possibility, but the loop test is your only way of knowing without pulling the chassis to view the circuit board. Even then, if you do not know what you’re looking for it will be hard to tell.
A recent MK III Black Dot surfaced with a serial of 15113 from 5/14/85. It had a DR 13 chassis code which may put the start of the MK III production to 2 or 3 of 1985 which would coincide with the last of the IIC+ production, but it may dispel the 12,500 to 15,000 serial number sequence. With a IIC+ in the 1406X range from 2/85, the C+ may not have even made it to 14,400. If it did, it may have been randomly sequenced in with the early MK III production. An inference to the actual monthly production from 12,500 from April 1984 to 137XX from October 1984 averages 200 units per month for the six month period. From late 137XX in November 1984 to 1406X in February 1985 the average drops to around 121 per month. With the MK III looming Mesa was definitely phasing out the C+ as orders for the III were being generated and amps being built as early as March 1985. Any C+ after March 1985 would have possibly been an attempt to use up the remaining stock and finally push production to the MK III full blast. Even if the IIC+ production was in full effect at an average 121 per month, the sequence would be about 14,370 to 14,400 as an inference. With new MK III orders and fewer MK II orders, the production slowed on average 79 amps less per month, thus reducing the amount of upper range IIC+ serial numbers. The final peek into the model change was the use of the 105-162318 power transformer on the first 150 or so MK III’s. When they were gone, the much smaller unit we know today was assimilated into production.

The End of an Era-

Asking why Mesa quickly went to the MK III is like asking why the earth spins. The circuitry and board design on the MK III was Mesa’s leap from the MK I style circuit boards and labor intensive manufacturing. It would have happened eventually. RCS is an amazing engineer, but an astute business man as well. As the PCB market moved forward with newer, cheaper techniques, so did Mesa. The extra savings may have been necessary to the companies long term survival as the orders increased the labor cost increased while the pricing stayed consistent. Saving an extra $ 300 per amp in production cost and still producing a bullet proof design was an outstanding achievement and allowed Mesa to move forward with future designs. Obviously, the stripes were a constant evolution to fine tune the III to player’s desires. With input from the chief designer, play tester and the brilliance from the Chief Technician the core team managed to sell around 13,000 plus units. With the three modes, we had our first glimpse of the future MK IV. The IV has lasted longer and sold more than any previous MK design. It may get to the point where it will pass them all combined unless the rumored MK V makes its debut soon and the IV is put to pasture.

Best Regards,

Edward P. Morgan

The Mark II-C FOOTSWITCHING SERIES- Pricing September 1984

Mark II-C Combo Amplifier with 12” Black Shadow Speaker

Standard 60 Watts, Vinyl Cabinet, Specify Black or Cream.
Slip Cover, SUS-4 Shock Mount & Lead/Rhythm Footswitch Set - $ 750
(Mark IIC 1X12 as above but without speaker $ 720 )

Performance Options Each Extra

Hundred Watt Chassis with Fan & 100/600 Watt Switch ………… $ 150
Simul-Class with Fan & Switch ( Add to 100 Watt Option) ……. $ 25
Reverb ……………………………………………………………… $ 150
Graphic Equalizer ………………………………………………….. $ 150
Electro Voice EVM 12” Speaker …………………………………... $ 70
Export Switch & Transformer (For All World Operation) ……….. $ 50

Cabinet Options Each Extra

Hardwood Cabinet with Wicker Grille …………………………….. $ 175
Hardshell Road Case with wheels, Black ……………………………$ 180

Mark II-C Amplifier Head, Top Only

Standard 60 Watts, Vinyl Cabinet, Specify Black or Cream.
Slip Cover, Lead/Rhythm Footswitch Set - …………………………$ 700
(18 ¾” wide, fits well visually on 1X12, 2X12 & 4X10 Cabinets)

Performance Options Each Extra

Hundred Watt Chassis with Fan & 100/600 Watt Switch ………… $ 150
Simul-Class with Fan & Switch ( Add to 100 Watt Option) ……. $ 25
Reverb ……………………………………………………………… $ 150
Graphic Equalizer ………………………………………………….. $ 150
Export Switch & Transformer (For All World Operation) ……….. $ 50

Cabinet Options Each Extra

23” wide cabinet – For Hundred or Simul ONLY (Black or Cream) $ 25
(Not available in Sixty – Fits well visually on 2X12, 4X10 & 4X12’s)
Hardwood Cabinet with Wicker Cane Grille (Either Widths) …… $ 155
Hardshell Road Case without wheels, Black (narrow chassis) ……. $ 115
Hardshell Road Case without wheels, Black (wide chassis) ………. $ 130


Coliseum Series 300, 180 Watts, 6 Power Tubes, Half Power Switch,
Vinyl Cabinet, 23” Wide only (specify Black or Cream) & Slip Cover,
(Can be wired for 117 or 230 volt operation.)

Mark II-C Type Series 300 Amplifer Head, includes Footswitch… $ 1000
Reverb ………………………………………………………………$ 150
Graphic Equalizer …………………………………………………..$ 150

Cabinet Options Each Extra

Hardwood Cabinet with Wicker Grille ……………………………..$ 155
Hardshell Road Case without wheels, Black……………………….. $ 130


Combo Amplifier with 15” EVM Speaker, Hundred Watt chassis with
Half Power Switch & Fan, Vinyl Cabinet (Specify Black or Cream),
Removable Casters & Slip Cover. Not Available in 60 Watt Model.

Mark II-C Type HundredWatt 1X15 w/EVM 15-4, Incl. Footswitch $ 1005
Simul-Class with Fan & Switch ………………………………….. $ 25
Series 300 Power Section ……………………………………………$ 150
Reverb ……………………………………………………………….$ 150
Graphic Equalizer ………………………………………………….. $ 150
Export Switch & Transformer (For All World Operation) ……….., $ 50

Cabinet Options Each Extra

Hardwood Cabinet with Wicker Grille …………………………….. $ 175
Hardshell Road Case with wheels, Black…………………………... $ 185

Mesa Engineering Price List – SEPTEMBER 1984

A gracious thank you goes out to Ian Dickey, Richard Ray, John Kamaly, George Stergiou Jr., Todd Duane, Joey B., Mike Bendinelli and to the hundreds of C+ owners that allowed me to invade their privacy.
Last edited by Boogiebabies on Tue Jul 28, 2015 6:42 pm, edited 20 times in total.

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Post by Stu Gutz » Fri Oct 19, 2007 9:00 pm

Wow! Great post man!!!


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Post by lesterpaul » Fri Oct 19, 2007 9:16 pm

bravo!Thanks !!
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Post by lockbody » Fri Oct 19, 2007 9:59 pm

Sticky material if there ever was one.

Great post!
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Post by Blueracer » Fri Oct 19, 2007 11:19 pm

Outstanding post. Second vote to make it a sticky.

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Post by Octavarius » Sat Oct 20, 2007 9:22 am

Fantastic! Thanks for the great info, Ed! :D

Mods, please make this a sticky! :D Finally we have a great guide on the board for everything about the IIC+ production!

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Re: IIC+ Guide for Dummies

Post by JOEY B. » Sat Oct 20, 2007 1:31 pm

Boogiebabies wrote:
The SP-11A and RP-11A were designed for the MK IIC. Their use was continued with the IIC+, Hence, the ability to upgrade from IIC to IC+.

Anything from 12,400 to 12,499 is a certain possibility, but the loop test is your only way of knowing without pulling the chassis to view the circuit board. Even then, if you do not know what you’re looking at you probably will not be able to tell.

Lots of useful info, Ed.
Any chance of preamp circuit board pics with highlighted verifications of a true C+ circuit?

This might help an online buyer of a supposed modded "C" or Coliseum model to feel more secure in their purchase (if they were provided the high-res photos), as they cannot try the loop test from across the country. :D
"One of these days, I'm gonna change my evil ways....... one of these days.

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Post by Boogiebabies » Sat Oct 20, 2007 4:30 pm

I'll probably put up a .Mac account with the circuit boards and the previous info.

I just basically could not get any further on the info, so why not post it.

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Post by Johnson » Sat Oct 20, 2007 11:43 pm

Great info! Thank you for compiling all of this great information! +1 on the Sticky!
84' Mark II C+ #1297X (SimulClass,Reverb,EV)
92' Blackface Dual Rectifier #39X

Rectifier Lineage:
IIC+ Guide:

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Post by jvk » Sun Oct 21, 2007 1:15 am

Very nice Ed! Look forward to your website. Now you can take a load off yourself and direct all those people with PMs towards your website :)

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Post by Boogiebabies » Sun Oct 21, 2007 10:32 am

Thanks Jonny.

Feel free to add it to the JVK site. It will probably help reduce the amount of questions from the UK C+ Mafia.

It's just a tidbit of observations, facts and endless waiting for certain amps to find there way to me.

I did not paste it correctly so I added the props section at the bottom. :D

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Post by Restless Rocks » Sun Oct 21, 2007 10:57 am

Very nice work Ed, look forward to seeing your Web site.

Rock On

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Post by Boogiebabies » Sun Oct 21, 2007 11:15 am

It sould be up in three years. :D

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Post by Buddy » Sun Oct 21, 2007 2:02 pm

:D :D :D :D :D Thanks Ed . :D :D :D :D :D

What , now I have to wrap my monitor in snakeskin ?
I almost spewed ale all over my key board , damn .

...And how can this be?

You are truly the kwezanart hatrack . 8)

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Post by PRS-Ian » Sun Oct 21, 2007 4:07 pm

Excellent job, thanks :D
Mk2C+ SimCl,Rev,EQ,EV,Export Transformer,Maple,
Mk2C+ 60W,Rev,EQ,EV,Imbuya
MK3 Blue SimCl,Rev,EQ,EV,Imbuya
Triaxis V2, 20/20, V-twin rack
Imbuya Open back Cab with EV
2 black tolex open back & 2 thiele cabs with EVs plus a Short Head Shell by GTS

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