How to understand the circuit board from schematics IIc+

[akamouzis]

Hey All,

i really really want to learn and understand each and every resistor/cap etc on my c+ but i can not read schematics. The actual circuit vs schematics look completely uncorrelated to the untrained eye and its especially more difficult when changes it resistor or cap values have occurred over the years.
Has anyone made a video going through every section of the board piece by piece and showing how it correlates to the schematics for a c+?
if not it would be priceless if someone could do that. Im looking at you Ed haha

Also random IIc+ questions:
the long heads with the presence knob on the front? were all those non reverb models? or coliseums? or coliseums with no reverb?
are non reverb IIc+'s missing one preamp tube from the circuit board?

 

[user 21540]

Even well trained techs have a hard time with Mesa's schematics. They are often hand drawn, go from right to left (which is the opposite of most other schematics) and also have corrections in them. I haven't seen someone go through a IIC+ but there is a guy here in Australia on Youtube who has gone into schematic detail with several Mesa amps over the years:
https://www.youtube.com/@BradsGuitarGarage/videos

 

[jrb32]

Hey All,

i really really want to learn and understand each and every resistor/cap etc on my c+ but i can not read schematics. The actual circuit vs schematics look completely uncorrelated to the untrained eye and its especially more difficult when changes it resistor or cap values have occurred over the years.
Has anyone made a video going through every section of the board piece by piece and showing how it correlates to the schematics for a c+?
if not it would be priceless if someone could do that. Im looking at you Ed haha

https://boogieforum.com/threads/mark-iic-to-c-steps-required-for-upgrade.83222/https://boogieforum.com/threads/mark-iic-schematic-correct.74680/(For reference this was an INFORMATION post and any repair work please send to Mesa if possible - being in Europe or Australia it's more understandable. Also I know you didn't ask about a C rather than a C+ or ++ but any conversion work is FULLY worth the cost. Although I think Mike B might have retired now and Mesa aren't doing upgrades anymore? Someone might be able to update me on this though)

Also random IIc+ questions:
the long heads with the presence knob on the front? were all those non reverb models? or coliseums? or coliseums with no reverb?
are non reverb IIc+'s missing one preamp tube from the circuit board?

Long heads can be loads of different models. Both non coliseum and coliseum. It's just to fit better in a cabinet stack. So in the process they moved some pots to the front instead of the back of the amp because there was now more room. That's it.

Non Reverb IIC+s are not missing a preamp. They just don't utilise that circuitry. Half of the 3rd 12ax7 and half of the 4th 12ax7 are responsible for the lead channel, and the other halves are responsible for the reverb. On the non reverb instead of designing a whole new design where the lead channel shares the same tube, it's still split between the two tubes but the reverb elements just aren't there. I haven't seen enough of those (SP10 and SP11) to comment further though on the exact circuit changes.

 

[Jay Omega]

Hey All,

i really really want to learn and understand each and every resistor/cap etc on my c+ but i can not read schematics. The actual circuit vs schematics look completely uncorrelated to the untrained eye and its especially more difficult when changes it resistor or cap values have occurred over the years.
Has anyone made a video going through every section of the board piece by piece and showing how it correlates to the schematics for a c+?
if not it would be priceless if someone could do that. Im looking at you Ed haha

Also random IIc+ questions:
the long heads with the presence knob on the front? were all those non reverb models? or coliseums? or coliseums with no reverb?
are non reverb IIc+'s missing one preamp tube from the circuit board?

Interesting idea, I wonder how many people would actually watch it.. Do you have any specific questions that I could answer

 

[meesa_jarjar]

Although I think Mike B might have retired now and Mesa aren't doing upgrades anymore? Someone might be able to update me on this though

I've been in contact with Mesa this week, I'm sending my amp in for service. Mike B is not yet retired but I think they're trying to funnel down the amount of service requests that end up on his workbench for his eventual retirement.

Mesa stopped doing any and all amp mods, at least for the general public, once Gibson took over.

 

[oogie]

Interesting idea, I wonder how many people would actually watch it.. Do you have any specific questions that I could answer

Specifically id like to know how the signal flows through the reverb circuit, but also generally just trying to understand how it all works and how the signal flows through the physical circuit board not the just the schematics.
Also can you look at the attached photo and tell me if i have the bright or dark version?

https://boogieforum.com/threads/mark-iic-to-c-steps-required-for-upgrade.83222/https://boogieforum.com/threads/mark-iic-schematic-correct.74680/(For reference this was an INFORMATION post and any repair work please send to Mesa if possible - being in Europe or Australia it's more understandable. Also I know you didn't ask about a C rather than a C+ or ++ but any conversion work is FULLY worth the cost. Although I think Mike B might have retired now and Mesa aren't doing upgrades anymore? Someone might be able to update me on this though)


Long heads can be loads of different models. Both non coliseum and coliseum. It's just to fit better in a cabinet stack. So in the process they moved some pots to the front instead of the back of the amp because there was now more room. That's it.

Non Reverb IIC+s are not missing a preamp. They just don't utilise that circuitry. Half of the 3rd 12ax7 and half of the 4th 12ax7 are responsible for the lead channel, and the other halves are responsible for the reverb. On the non reverb instead of designing a whole new design where the lead channel shares the same tube, it's still split between the two tubes but the reverb elements just aren't there. I haven't seen enough of those (SP10 and SP11) to comment further though on the exact circuit changes.

Attached are pics of c+ i just bought today (not delivered yet) with no reverb and seems to missing a tube, although i do understand there should since v3 and v4 serve both the lead channel and reverb when its there but i dont see it.
can reverb be added?

this thing is in desperate need of a thorough cleaning and possible refurb, hope Mike stays around just a bit longer.
.

 

[Henz]

Specifically id like to know how the signal flows through the reverb circuit, but also generally just trying to understand how it all works and how the signal flows through the physical circuit board not the just the schematics.
Also can you look at the attached photo and tell me if i have the bright or dark version?

Attached are pics of c+ i just bought today (not delivered yet) with no reverb and seems to missing a tube, although i do understand there should since v3 and v4 serve both the lead channel and reverb when its there but i dont see it.
can reverb be added?

this thing is in desperate need of a thorough cleaning and possible refurb, hope Mike stays around just a bit longer.
.

Though I don't have much experience with the sp11 , lots of experience with the rp11, after viewing V3 , it appears that this amp does not have the bright reduction mod. This amp has some very neat and tidy lead dressing.