HighWattGuitars
Member
Thanks for all the work that you put into this. You've created a very useful set of reference material.
Putting together a Mark III Guide
- Thread starter jrb32
- Start date
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Thanks! To sum up in a general way schematic wise:
Black - Essentially the original schematic based off the incorrect IIC+ schematic with R130 and R126 for R2 channel. C214 added in later for R2 channel.
Purple - A black stripe with basically a IIC+ lead circuit minus a few slight component value changes. But then C26 removed to make it less like a IIC+ in the EQ section... very underlooked amp. Easiest to + mod in my opinion.
Red - A purple stripe but some weird preamp values going on. Lead circuit now almost identical to IIC+. R2 channel changed to remove R126. In its place sticks in an automatic treble shift to be enabled when in R2 mode via an additional LDR.
Blue - 2.2M for R106. Crazy gain lead channel that was completely overhauled. Same R2 channel as Red. Power section finally has 0.0047uF presence cap and 1.5K presence control resistor (same as IIC+)
Green - same as a blue but has 3.3M for R106. Outer simul power valves wired in pentode.
Black - Essentially the original schematic based off the incorrect IIC+ schematic with R130 and R126 for R2 channel. C214 added in later for R2 channel.
Purple - A black stripe with basically a IIC+ lead circuit minus a few slight component value changes. But then C26 removed to make it less like a IIC+ in the EQ section... very underlooked amp. Easiest to + mod in my opinion.
Red - A purple stripe but some weird preamp values going on. Lead circuit now almost identical to IIC+. R2 channel changed to remove R126. In its place sticks in an automatic treble shift to be enabled when in R2 mode via an additional LDR.
Blue - 2.2M for R106. Crazy gain lead channel that was completely overhauled. Same R2 channel as Red. Power section finally has 0.0047uF presence cap and 1.5K presence control resistor (same as IIC+)
Green - same as a blue but has 3.3M for R106. Outer simul power valves wired in pentode.
s-fresh
Well-known member
Really impressive work. Not sure what I will ever do with this information having Mike and Mesa in my backyard, but still awesome to have on file for when he eventually retires.
Exactly I'm not sure what will happen with regard to III+ mods or even IIC+ maintenance or C upgrades after Mike B retires. Plus it's nice to document these old amps as much as possible
I'm sure Mesa have all information on file it just depends if they choose to continue doing the work with another person in place. I would imagine they will still do repair and maintenance but probably stop the + mods on the C and III.Moving onward as a guide, there is a Reverb mod/fix done at the factory. If this was done there will be a big R written on the back. This essentially adds a 120K 2W resistor from R116 to ground. I'm not 100% sure on the reason for this but it's supposed to sort an issue with the reverb distorting or causing interference. Personally I have also found you can get a popping noise on the speaker sometimes causing interference without this 120K resistor in place. The fix hasn't got anything to do with increasing reverb strength and, in my experience, it does change the overall tone of the amp and I wasn't a fan.
Some people say you can sort this reverb issue by moving the reverb tank around 180 degrees so the reverb tank plugs are no longer under the power transformer. I ended up removing this 120K resistor and made the voltage rail going to R116 from C to B on the schematics. I did this with running wire off the B rail 30uF cap to R116 with one leg of R116 lifted off the board going to this wire and this got rid of the popping or distorting issue and for all and made the reverb all so sweet. This B rail is how it's done in the C+. I'd recommend upping R116 to a 2W resistor though in this scenario.
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Mike B. can’t retire until he mods my Studio Preamp and Mark lll HRG!
diancarlo81
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Hoping a guide for III+ (schematic)... Thanks!
lovetoboogie
Well-known member
Outstanding work and effort my friend. This will really be useful to help keep Mark III's up and running. And more importantly to respect their differences when doing service work. Quite impressed!
truongbilico
New member
This is just great!
I´m looking forward to see this.
truongbilico.
I´m looking forward to see this.
truongbilico.
candletears7
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jrb32 said:
Amazing work. Thankyou!
If I wanted to take my MKIII No-Stripe/Black Dot to IIC+ specs, which IIC+ schematic should I refer to to make the above changes?
Re: Mark III to Mark II mod
Post by jrb32 » Tue Jan 29, 2019 9:50 am
3rd post from bottom
http://forum.grailtone.com/viewtopic.php?f=3&t=83605&start=15
Any mistakes you come across feel free to edit and let me know. Easy to compare the two and go from there but the rules are:
A) Send it to Mike B if you're in the USA.
B) Do not attempt unless you have a lot of electronics or soldering experience and cannot send it to Mike B due to geographical location. Lead solder. Iron set to 410 degrees C. The traces can be easily damaged and might need to be repaired. Having a III+ mod not done by Mike B may harm its resale value.
C) The 22K cathode resistors can be left as 22K. Close enough to 15K but you can change them to 15K if you want.
D) Orange drop type (225P vs 715P) resistor type and tantalum cap type vary between IIC+s, especially the orange drops in the power section it seems.
E) For a ++ switchable mod I like to add a 100K resistor off the treble pot with R2 to use C214 only with a 15uF cap instead of a .47uF. You might be able to do something more clever though with the relay.
F) Don't add in the extra D+ voltage rail. It's messy and not worth it.
G) DO add in the B voltage rail for the Reverb like on the C+. It makes a big difference separating this from the other 12AX7 power rails and don't get any interference that the III 120K 2W factory reverb mod tried to address. You have to run a wire though.
Cheers,
Jon
Post by jrb32 » Tue Jan 29, 2019 9:50 am
3rd post from bottom
http://forum.grailtone.com/viewtopic.php?f=3&t=83605&start=15
Any mistakes you come across feel free to edit and let me know. Easy to compare the two and go from there but the rules are:
A) Send it to Mike B if you're in the USA.
B) Do not attempt unless you have a lot of electronics or soldering experience and cannot send it to Mike B due to geographical location. Lead solder. Iron set to 410 degrees C. The traces can be easily damaged and might need to be repaired. Having a III+ mod not done by Mike B may harm its resale value.
C) The 22K cathode resistors can be left as 22K. Close enough to 15K but you can change them to 15K if you want.
D) Orange drop type (225P vs 715P) resistor type and tantalum cap type vary between IIC+s, especially the orange drops in the power section it seems.
E) For a ++ switchable mod I like to add a 100K resistor off the treble pot with R2 to use C214 only with a 15uF cap instead of a .47uF. You might be able to do something more clever though with the relay.
F) Don't add in the extra D+ voltage rail. It's messy and not worth it.
G) DO add in the B voltage rail for the Reverb like on the C+. It makes a big difference separating this from the other 12AX7 power rails and don't get any interference that the III 120K 2W factory reverb mod tried to address. You have to run a wire though.
Cheers,
Jon
chipaudette
Well-known member
All of the links appear to be broken. 404!
Re: Putting together a Mark III Guide
Post by jrb32 » Wed Feb 06, 2019 6:50 am
http://forum.grailtone.com/viewtopic.php?f=3&t=83605&start=15
3rd post from bottom click link
Post by jrb32 » Wed Feb 06, 2019 6:50 am
http://forum.grailtone.com/viewtopic.php?f=3&t=83605&start=15
3rd post from bottom click link
Jon
The links are working fine, I tried to cut and paste a post of yours and the links dont work but the original links are fine
The links are working fine, I tried to cut and paste a post of yours and the links dont work but the original links are fine
McBarry
Well-known member
Haven't been on for a while, but quick shouts to all U guys for TRULY STUNNING work..!!
Level of detail, sense of support for this amp but also M/B..
Big high 5's all round - of course maintaining social distance tho'..!!!
Cheers, Dave
Level of detail, sense of support for this amp but also M/B..
Big high 5's all round - of course maintaining social distance tho'..!!!
Cheers, Dave
alanlcohen
Member
Just adding my two cents. I currently own a Red stripe modded by Mike B. and have owned both Blue and Green stripe Mark IIIs. You are spot on in describing the Blue's Lead channel; its a beast to wrestle with, a little over the top for my tastes. Curiously in the evolution of the MKIII I found the Green stripe the least appealing of the three. The Green stripe's clean was sterile and the Lead & Crunch modes lacked bounce (great for Metal, but ear fatiguing for over styles). Both the Red and Blue stripe featured warm Clean channels and the other modes have bounce or are more dynamic/responsive than the Green stripe. So take this all variance of tubes & speakers used. Thanks for posting.
This thread has been awesome. I am planning to pickup a III. I could go a lot of directions on the strip but I have been leaning blue, red, or green. The thing is I see a purple stripe that I can pick up with a return window on it, but the purple kind of sound like it would be the lest fitting option for my taste.
So the question is should it be possible to effectively have a purple stripe modded by a local tech into a blue or red stripe for fairly cheap? I already know I would be looking to do the R2 volume mod and the amp might need a general servicing as well, so the stripe conversion would be easy to tack on as long as it was possible and should not cost much. I live in Houston and Mesa has a certified repair center that is nearby, so that was my thought to save on shipping costs into Mesa. If that would be required, then I’ll just continue to wait for the perfect model to pop up. But I the ability to buy now and return if needed has its merits.
So the question is should it be possible to effectively have a purple stripe modded by a local tech into a blue or red stripe for fairly cheap? I already know I would be looking to do the R2 volume mod and the amp might need a general servicing as well, so the stripe conversion would be easy to tack on as long as it was possible and should not cost much. I live in Houston and Mesa has a certified repair center that is nearby, so that was my thought to save on shipping costs into Mesa. If that would be required, then I’ll just continue to wait for the perfect model to pop up. But I the ability to buy now and return if needed has its merits.
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