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Schematic of a Messa Mark IIC+


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8/4/1998 6:53 AM
Nick
Schematic of a Messa Mark IIC+
Anyone has schematic of the Mark IIC+ ?  
Please would you send me a scan  
( to my e-mail ) .  
I could trade for it too.
 
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8/12/1998 4:29 AM
Jupa

Hi,  
 
I recall this could be found in Groove Tubes Tube Amp Book. Im not sure if the name was correct but anyway its a GT book with lots of tube amp schematics, also Mesa Boogies.  
 
Jupa
 
8/12/1998 7:29 AM
Richie

Most of the mesa boogies are in the volume 4 tube amp book the mark IIc+ is on page 713. I don't have any way to send a schematic,I wish there was someone, ampage, that would list all these schematics,people could send in the ones not listed.That would be a great resource of info,it would help everyone,they could also list other info on amps that is hard to get. hope this helps you. [Richie]
 
8/12/1998 10:54 PM
Steve A.

Richie:  
 
    Can you identify the 2 power amp/power supply drawings on pages 714 and 715? Or at least tell me which one would go with the IIC+?  
 
Steve Ahola  
 
P.S. The GT book has SO many schematics for under $30 that everybody should have their own copy... But there have been a lot of requests for scans of the Boogie amps so there may be a link posted here soon (it'd help if I knew for sure which power amp drawing to include).
 
8/13/1998 3:57 PM
Richie

Steve: That is a good question, I would hope it would be the page after 713,it would seem logical to have the power amp section after the preamp page, but I don't know for sure.The only differences in 714 and 715 are a few resistor values in the bias supply,and eq section,and also changing the heater circut to DC.If you knew if the circut of the amp for this section,you would know which one it should be.I have not worked on this amp so maybe someone else would know for sure.I like a few parts on the schematic that show resistors,and instead of the value it says factory select!also at the bottom of the page it talks about beware infringers!And they have sued people and put them out of buisness!I think these boogies and a lot of other amps were copied from fenders,I wonder how they feel doing the same thing. [Richie]
 
8/14/1998 1:48 AM
Steve, again
Anybody else know which power amp schematic goes with the IIC+?
Richie:  
 
    Other threads here have mentioned that Mesa would intentionally leave mistakes in their schematics just to throw off "pirates". (Don't worry, Randy- Victoria only copies tweed Fender amps!) My own interest is educational- I like to study what R. Smith and others have done, try them out in various amp projects and then modify them to my own personal taste. By the time I'm done, they are quite different from the original circuits, but the influence is definitely there...  
 
    The "factory select" on the resistors in the bias supply does appear to be legit. Since the amp does not have a bias adjustment they probably changed the values of that resistor to match whatever output tubes that they were currently using. (An AMPAGER would probably add a bias pot or two anyway so that shouldn't create any problems here.)  
 
    Another difference between the schematics on page 714 & 715 of the Pittman book is the "Rhythm 2" switch and footswitch on page 715. That clue may jog someone's memory! (P.S. I think that the heaters on page 715 are AC, but they are using the 6.3vac tap through the bridge rectifier to run the dc relay coils.)  
 
Steve Ahola
 
8/14/1998 5:32 AM
GFR

The Mark II is a two channel amp (Lead and Rhythm). The Mark III that is on page 716 is a three channel amp (Lead, Rhythm 1 and 2). So if you inspect the channel switching circuitry in pages 714 and 715, the conclusion would be the following:  
Pages 713,714 - Mark IIC+  
Pages 715,716 - Mark III  
 
The Mark IIC+ and Mark III are almost identical. The lead voicing is a little different. The Rhythm 2 is a variation on Rhythm 1 by putting another 3M3 in parallel with the one present since this circuit was called "blackface preamp". The difference in volume is dealt with a fixed attenuation resistor after the next gain stage. This fixed attenuation never pleased users, so changing the value of this resistor is a standard MESA mod. If you can find place in the chassis for another pot, replace it with a Rhythm 2 Master Volume.  
 
See Gil Ayan's page for a great description on how the Mark series evolved. I posted the URL in the misc forum some time ago.  
 
In MESA's site there's an article from Randall Smith where he tries to explain why his amps don't have bias pots. In the Pittman book there's a mod to add a bias pot to these amps.  
 
GFR
 

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