Mesa Boogie Mark IIC: Cathode Bypass Cap and Resistor on V1B

[richiealv]

I have a Mark IIC Coliseum 300 series, buddy do you think you can email me the schematics of this amp please? I will really appreciate it, mine stopped working yesterday and needs maintenance... This is my email: ricardoalvaradocr@gmail.com 

[JCKCPA]

I have a rare Mark IIC "i". It has reverb and no eq. I tell you it will never ever

get the "+" upgrade. The sound is articulate, real, punchy, and absolutely

amazing. I believe the vintage boogies are the best esp without the eq.

Mine has a special coding on the chassis to keep it from oxidizing.

It is absolutely prisine and I am convinced it is and sounds better than

any IIC+. It is tight and really clean sounding. The Mark IIC "i" is right

before they switched to the IIC+.

[josemi21]

I own a mark iib and the tone is great, whats the difference between iib and iic?? I am not clear about that, there are lots of theories but I would like to know the real difference.

[chipaudette]

@josemi21

The Mark IIB is indeed different than both the IIC and the famed IIC+. The biggest differences are in the lead channels. So, if you dislike the lead channel on the IIB, you may like the IIC or the IIC+. They're just different (somewhat different tone shaping, different voltages on the tubes, different amount of gain).

The clean channels, however, are more similar than different. If you dislike the clean channel on the IIB, you'll probably dislike the clean on the IIC and IIC+.

[chipaudette]

@josemi21

I misread your comment. I thought that you said that you did NOT like your IIB. If you do like your IIB, you will probably like the clean channel of the IIC or the IIC+. The lead channels, though, are somewhat different than your IIB. They're not as different as a Marshall, but they are different. The IIC is also quite different than the IIC+. The IIC+ has more gain and more of an upper-mid focus to the gain. As a result, it has a more liquid feel.

[Golfinnder]

I don´t understand Mesa Boogies, can you explain me..? are the MB Mark IIC or IIC+ maded by the people or are they marketed?

[chipaudette]

@Golfinnder

The Mesa Boogie Mark IIB, IIC, and IIC+ are all vintage amplifiers made from the early 1980s to the mid 1980s. They were all made by Mesa Boogie in California, USA. They are no longer in production.

[AlembicVapor]

MESA routinely mislabels their schematics. I spoke with Rick at SIB, and he said that some of their schematics appear to be intentionally mislabeled... He said that according to one schematic, there's no way the circuit could operate the way they had it mapped-out. Weird! I have a Mark IIC myself, that was upgraded to a Mark IIC+.

[chipaudette]

@AlembicVapor

Yeah, I've heard the same thing. There was no IIC schematic on the web, so I traced it out and made my own. I've since sent this amp to Mesa to get it upgraded to a IIC+. Once I got it back, I traced out its new circuit and compared it to the schematic on the web. The web schematic was actually pretty decent. Well, they did re-arrange the tube sections (using V4B instead of V2B and such) but that *shouldn't* affect the tone.

[coltar1234]

that looks scary haha

[drewswebsite]

Also...My preamp board is an RP 11A and the amp is not a "+"

[jcoopercam]

Does the Mark IIC+ also use the RP 11A board?

[drewswebsite]

chipaudette

I have the same caps and resistor that you are pointing out. I ordered the new amp directly from Mesa Boogie 7/25/1983. At that time Mesa would let you order an amp with a small down-payment (mine was $150.00!) and pay the balance off over time as/when you could afford it. My initial order was for the Super Sixty 60 Watt Model with reverb and a Black Shadow. I later added the Graphic EQ ,2 foot-switches and a road case. In May of 1984 I paid the amp off and took delivery. DrewV

[chipaudette]

@drewswebsite

So, your post was a long time ago, but after this video, I kept on probing the amp. It turns out the Mark IIC pulls the effects loop off the cathode of the V1B, which is way early compared to every other amp. This puts it BEFORE the overdrive circuit, which is not useful if you like some echo/delay on your lead tone. The 0.1uF cap and 15K resistor that I point out in the video are the branch off to the effects loop. FYI.

[drewswebsite]

@chipaudette My amp was sounding bad. The reverb sounded crappy, the overall amp tone was pathetic. I decided to "blueprint" the Boogie. I found a handfull of out of spec components. Some in the reverb circuit, most on the preamp board including one orange drop near V 3. I replaced all of the electro caps. Finally I cleaned all ins/outs, pots, graphic EQ sliders and tube socket contacts ( and retensioned as needed) Result: A totally new sounding amp, full response and tone! Drew