Mark IIc mods/upgrades

[Joelschaos]

Hi guys. I have a few things here... firstly I own a very late mark IIc 60 watt head. It has a serial of 11803, and is one of the transitional models that has a IIC+ face plate (pull deep over master pot). I saw on another thread that people here were looking for pics and info on original IIc's because they barely exist anymore, since people are all upgrading to the IIc+. If anyone is interested in some pics or information on the circuit boards, I would be happy to offer my assistance.

Secondly, I am interested in upgrading my amp if possible. I am a PACE certified solder technician and am quite proficient in electronic repair. I stumbled across this site and was wondering what you guys thought of it:

http://www.associatedcontent.com/article/1969488/converting_the_mesa_boogie_mark_iic.html?cat=33

I haven't actually had a chance to verify all that is written there but it looks pretty interesting.

Beyond that, my amp is about 26 years old and I have gigged with it alot... every once in a while it gives off some crackling or buzzing, even if there is no guitar plugged in, and the tubes are new. I was wondering if it is about time to change out the caps. If anyone has any info on doing this, and maybe could give me advice or guidance that would be great.

Thanks again
Joel

 

[Boogiebabies]

Do you have the RP-10, RP-11, SP-10 or SP-11 circuit board ?

 

[JD]

I drew the picture but I didn't post the guide it wont help you with a Mark 2 C to mod to a + is alot more involved
this is a guide to mod a studio preamp closer to C+ specs I was comparing schematics of the two assuming the schematics are correct. works great with a studio preamp but will not work for a Mark 2C

 

[JOEY B.]

I was comparing schematics of the two assuming the schematics are correct.

You know what happens when you ASSUME something, right?

 

[JD]

sure do

 

[chipaudette]

I had a IIC. I traced out its schematic. Then I sent it to Boogie for the upgrade to the IIC+. Then, when I came back, I traced out most of its new schematic. The IIC schematic is quite different than the IIC+. In fact, depending on your view of the (pre-amp) world, the IIC is a freak in the Mark II line.

Here's my post that includes links to the schematics. This post was from BEFORE I sent my amp off to Mesa...

http://forum.grailtone.com/viewtopic.php?f=4&t=39528

Note Boogiebabies comment in the thread above about cramped spaces and amp butchery. Please consider his comments before doing the work yourself.

Chip

 

[Boogiebabies]

The earlier RP-11 boards traces were not as thick as the later ones. Good enough, but easier to damage with too much heat.

 

[Joelschaos]

Okay guys, sorry I took a little while to get back. Here are some pics of my amp, and some info to follow...

On the side of the chassis is written either "5" or "S" in the middle, with a small "34" in the bottom corner. On the top of the chassis is written "6827" (you can see it in the last picture, right above the lead drive pot). The pre-amp board says "SP-10", made in 1983. The power-amp board says PWR-7D1.

Hopefully this can give you guys some background in identifying my amp and what I can do with it. Some other questions... what is the 1/4" jack on the bottom of the chassis for? Why does one 12AX7 plug into the power-amp board? Which caps are the ones that need replacing? Any info would be very appreciated!

Thanks!
Joel

 

[Boogiebabies]

Okay guys, sorry I took a little while to get back. Here are some pics of my amp, and some info to follow...

On the side of the chassis is written either "5" or "S" in the middle, with a small "34" in the bottom corner. On the top of the chassis is written "6827" (you can see it in the last picture, right above the lead drive pot). The pre-amp board says "SP-10", made in 1983. The power-amp board says PWR-7D1.

Hopefully this can give you guys some background in identifying my amp and what I can do with it. Some other questions... what is the 1/4" jack on the bottom of the chassis for? Why does one 12AX7 plug into the power-amp board? Which caps are the ones that need replacing? Any info would be very appreciated!

Thanks!
Joel

The S is for 60W/Sixty Watt. The 34 may be the week of production in 83 and the 6827 may be a purchase order number. The 1/4 jack with the yellow wire
to the Lead Master should be a preamp out/ power amp in jack. The preamp tube on the back board is the phase inverter. In any reverb equipped amp there is no more
room between the transformers for a fifth preamp tube so Mesa put it in the back. For non-reverb amps, there is just a hole in the chassis. The extra switch in the back is for the 117V fan supply that is being hijacked off the PT primary. It is not stock as 60W did not come with a fan. Looking at the circuit, it's a IIC. You can run the loop test to double check, but I'm 99% sure it's a IIC.

 

[Joelschaos]

The S is for 60W/Sixty Watt. The 34 may be the week of production in 83 and the 6827 may be a purchase order number. The 1/4 jack with the yellow wire
to the Lead Master should be a preamp out/ power amp in jack. The preamp tube on the back board is the phase inverter. In any reverb equipped amp there is no more
room between the transformers for a fifth preamp tube so Mesa put it in the back. For non-reverb amps, there is just a hole in the chassis. The extra switch in the back is for the 117V fan supply that is being hijacked off the PT primary. It is not stock as 60W did not come with a fan. Looking at the circuit, it's a IIC. You can run the loop test to double check, but I'm 99% sure it's a IIC.

Great! I already performed the loop test, I know it's a IIc (not +). I know the fan isn't stock because I was the one who added it. =)

So do you know all that Mike B. can do to this baby? I'm guessing he could basically overhaul it... add reverb, eq, upgrade to IIc+, maybe change out the caps? For any of you who have had this done, what does he charge and how long does it usually take? Ever have any problems?

Thanks
Joel

 

[Boogiebabies]

A full cap job and upgrade would probably run around $500-600 at Mesa.
Call Mesa and ask for Ext. 329. Mike will tell you what he can do regarding
mods, EQ upgrades etc..

 

[Joelschaos]

A full cap job and upgrade would probably run around $500-600 at Mesa.
Call Mesa and ask for Ext. 329. Mike will tell you what he can do regarding
mods, EQ upgrades etc..

Thanks so much! I will call. If I go ahead and do it I will post pics once I get it back.

 

[Boogiebabies]

A full cap job and upgrade would probably run around $500-600 at Mesa.
Call Mesa and ask for Ext. 329. Mike will tell you what he can do regarding
mods, EQ upgrades etc..

Thanks so much! I will call. If I go ahead and do it I will post pics once I get it back.

Good luck. You have the "Pull Deep" face plate, what's the tech date on the amp ?

 

[Joelschaos]

Good luck. You have the "Pull Deep" face plate, what's the tech date on the amp ?

From what I have read the "tech date" is supposed to be located on the underside of the chassis, handwritten, correct? I have looked, there is nothing written except for the tube types. The only writing on the chassis is what I have quoted earlier except of course for the MB initials.

 

[Boogiebabies]

Thanks, just trying to see when they started using those faceplates. Mesa had them before Dec. 1983.

 

[Joelschaos]

Thanks, just trying to see when they started using those faceplates. Mesa had them before Dec. 1983.

Yeah, I know there are some discrepancies as to when they started using these faceplates, as there are amps made later than mine that still have the "gain boost". My amp is clear proof that "pull deep" printing isn't enough to call it a C+. From what I hear, there were just some older faceplates left over, and they were using older as well as newer ones at the same time. That makes sense to me. As to when the first "pull deep" faceplate was used, I think that will remain somewhat cloudy. My serial is 11803 if that helps. I don't know how my number relates to the earliest "pull deep" known so far.