Mark llB - difference between early and late models

[Rob Lockwood]

I have a late model 1983 Mark llB. I bought it because my favourite Boogie sounds came from the clean-ish channel of an early Mark llB with a few pedals in front. This amp had a gorgeous slightly overdriven and compressed sound on the clean channel with a nice, fat 'singing' upper mid range. My 1983 Boogie is a great amp but has never got close to that sound on the clean channel, so recently I was going through some youtube vids of Mark llBs. There was another 1983 model and it sounded just like mine with a nice clean bright sound on the clean channel not too far off a Fender twin. Other earlier amps had that overdriven and compressed sound similar to what I remember. The only difference I was aware of was that on later llBs the treble shift is only available on the lead channel where it is available on the clean channel on the earlier amps. I opened up my amp to look at how the switching for that was done and how I could add a switch to give the option of having treble shift on clean. I have ended up tracing the whole preamp through to draw up a schematic, a job which is still work in progress. But what I have found so far is that the 1983 Mark llB is a quite different amp from the earlier models based on a schematic available online dated 1981 and some good photos on here of the insides of an earlier llB. As well as treble shift being switched out in clean the gain boost is completely different. Instead of lifting the tone stack out of the circuit to get a boost, the 1983 llB boost works on V2b cathode resistor same as the Mark llC+ does. As this is after the tone stack, unlike the earlier llB the tone control will still work normally when gain boost is pulled. On early llBs the amount of reverb is change when switching channels but on the 1983 those relay contacts are used to switch treble shift, so reverb switching isn't done.

What is interesting is that although I am really interested in the early Boogies and have read hundreds of post here and elsewhere about the llB model and the history of the Mark series I have never picked up anything to suggest that there were significantly different versions of the llB through its production run. My recent work on schematics and experience with the actual sound suggests that the later 1983 llBs with the RP-2C pre-amp boards are quite different amps from the earlier models. Although I don't have a schematic of a llC I suspect that at the end of the llB run Mesa were trying out changes that would be made on the llC model.

Has anyone else experienced this difference between early and late llBs?? Can anyone confirm my findings that the later 1983 amps sound different to the earlier ones? I like my amp and the clean sound is great, better for some purposes but I suspect that for the sound I want I need to track down an earlier model of llB.

 

[jrb32]

Can't comment but IIC schematics and pics are here: https://get.google.com/albumarchive/109244885492088240430/album/AF1QipOOvvzkvLQUbm059tNozq5FOxs65a210OleNBTQ?source=pwa

(not mine unfortunately!)

Would be great if you could share any schematic you've traced of the IIB. I'm really interested in tracing the evolution from the IIA to the III in all its various forms.

Thanks,

Jon

 

[GM1]

Rob,

I have a 1981 MRK II B combo and just purchased a 1983 MRK II B combo revision C with the RP 9C board. I too want to hear the differences as I am curious about the evolution of the MRK II B series. Will post more info once I receive the amp. As a caveat I only use the clean channel on my amp I don't really have a need for the lead channel so don't have much experience with the lead side. There are so many great pedals these days to work with I don't need or use the second channel. BTW mine was listed as an RP 9C board - guessing there were changes based on the numbers?

 

[Don]

I'd like to see your schematic to compare to my MK IIB from about 1981. It has RP 8C on the board. This amp has a slightly overdriven clean channel. Kind of like a "Dumble" type of sound. Dirty without being gritty. Smooth. It doesn't have a lot of drive in the lead channel unless everything is cranked and most of the pots are pulled.

I had read that none of the MK IIBs matched the published schematics, that the schematic was hastily drawn up using an older schematic.

 

[GM1]

So I received my 1983 MRK II last night and had a chance to compare clean channels with my 1981 MRK II. Both sound about the same however the gain structure is different. The 1983 has to be turned up higher on both the master and volume to match the 1981. Both amps are the same meaning EV speakers and 100 watts. I ran both using my Brown Box with a 3% reduction in voltage so they run at about 115 volts in my studio. Could just be the tubes but there is a difference. As mentioned I don't use the lead channel so don't have much to offer beyond how the clean channels compare. On both amps the presence control makes a big difference. Reverb is OK on these amps. Im not a big reverb guy I know there is much better in todays world but these do just fine to my ear. Funny one is a wood cab the other is black tolex. Thought the wood cab wood be a lot heavier but it's really not.

 

[jrb32]

Amazing info! Any chance you could upload any detailed pics of the RP8 and RP9 boards? Since my earlier post on here I've managed to trace and map out the RP10 and RP11 boards for the IIC/C+ and all the Mk III boards along with schematics. Trying to document and date the development of the early Mk models as much as possible and share on here for as much info as possible on these early greats!

 

[GM1]

Having spent more time with both my 1981 and 1983 2B combos there is no question the 1983 version sounds different compared to the 1981. As mentioned earlier the gain structure is very different and the midrange is different. I spent an hour plus last night trying to get the 83 to sound like the 81 but just couldnt get it. Mainly the midrange can't be dialed the same - the 83 has what seems a wider Q on the midrange control and so it can"t get quite as tailored. The 81 has this top end sparkle and chime that the 83 is missing (on the clean channel) Maybe different tubes could get them closer I don't know but suspect the board changes made over time ( 81 - 83) have had an influence on the clean channel tone. I prefer the 81 without question. The 83 lacks some character on the clean which you might not hear if you didn't have the two amps side by side. I will experiment with some tubes but suspect I won't keep the 83 and instead look for another 81 combo. I would like to have two that sound the same - one for backup.

 

[CrustyBooger]

Rob,

You are indeed correct. The late IIB has a 9C pre-amp board (your 83 was likely a transitional B, with later style knobs). Contrary to some conventional wisdom, the pull deep function was introduced in the Mark IIB and the 9C board has it; the face plates just continued to say gain boost until the C to C+ transition.

The when pulled, it uses a more classic frequency shelf (9.3Hz 1.5R/.22mfd) n the FX return V2 triode, and when the knob is pushed in, it changes the 3db cut off shelf to remove low frequencies and increases headroom. If you are going for a more fender frequency response and play mostly clean/low gain, you might want to run with it pulled out to avoid cutting off the low end.

I am effectively the original owner of one of the last few IIBs (108XX range), and for years expected it to work like the gain boost on the earlier versions, and so, I thought it worked poorly given that. I found out the joke was on me when years later I had the amp on Mike's bench and was shooting the poop about some mods I wanted when he was doing the "B+" fix and he confirmed that it was the pull deep circuit instead! With decades of tech-ing my own equipment I had never bothered to trace the circuit--the amp has been that reliable!

They found the tone stack lift you see in the schematic was problematic. At high gain levels with contemporary tubes you would find micro phonics to be a real problem. So in typical fashion, they just repurposed the pull switch into something more useful (and maybe avoided an outcry from the folks that wanted gain boost!).

As to the treble shift knob, that was designated as a lead EQ enhancement on yours; you should be able to trace back the tail of the cap and change how it completes its circuit if you wish. Alternately, you could voice the amp differently if you want to extend the treble down a bit.

You will find that there were not just two versions of II between the start of A and end of B (or any model transition)--Boogie was always progressing the design and changing things that did not work out, were not popular or were problematic. Thus there is a some sonic differences through the range on top of individual amp differences.

 

[MK IIB]

Interesting post and one I can identify with..Also some very informative information from "CrustyBooger" above...

I have a 1981 mark IIB that I love..It's the straight model...No EQ/reverb and 60 watts (Export Transformer)

It has a lovely warm sound and the clean channel breaks up lovely and is quite "gainy" at higher volumes on volume 1 so much so that I made a video to ask other IIB owners if theirs behaved the same way..as although I liked it..I wasn't sure if it "should" be like that

About a year ago a 1983 Mark IIB in good condition and for a fair price came up for sale(They don't come up all that often in the UK)
It had Reverb and EQ and the EV 12L (still 60 watts)and I thought great...An upgrade with the EQ etc and at least a great spare to have..

This amp could not have sounded any different to my mark 1981 IIB..The clean channel stayed totally clean with volume 1 at 10 but it was a very "sterile" clean and very trebly...almost ice picky?

The presence circuit on mines is fantastic...the range from 0-10 is huge on the '81..Between 0-3 you get a lovely warm tone..
The presence on this one was no where near as effective and I couldn't really dial out the harsh treble...(Only with the EQ)but still had a slightly harsh sound and the lead channel was also no where near as nice sounding as the '81...

I passed on the amp after traveling quite a bit to buy it...I felt bad for the seller but it was a completely different amp...
I thought a Mark IIB was a Mark IIB if anything I thought it would have sounded better..with the EQ etc..I have often wondered if I made a mistake not taking it and if tubes etc might have helped..but yeah it was nowhere near as nice sounding as my '81 model...and didn't have the same feel

Incidentally the treble shift only works on the lead channel on mines too?Is it not the other way around?Is it not the later amps that had the treble shift available on the clean channel too?

Here's the little video I made of my clean channel..I love what it does but I was wondering if it should have had as much gain on the clean channel but other users thought it was just fine?If I want Fender clean I simply have volume 1 at around 5.

Excuse the playing...I'm just sitting messing around. https://www.youtube.com/watch?v=V6xMQY_2Wtc

 

[TiPiMods]

Very interesting, I never heard that there are different Mk IIB versions. I have a IIB SRGX from 7/6/81 with the RP 9A board, so it seems the change from the 8C to the 9A board must have been in about that time period. As expected, mine has the tone stack boost and treble shift works only in lead mode. I recently had to change the caps of the power supply and made some fotos of the board, yet have to find a way to post them here.

 

[TiPiMods]

Interesting post and one I can identify with..Also some very informative information from "CrustyBooger" above...

I have a 1981 mark IIB that I love..It's the straight model...No EQ/reverb and 60 watts (Export Transformer)

It has a lovely warm sound and the clean channel breaks up lovely and is quite "gainy" at higher volumes on volume 1 so much so that I made a video to ask other IIB owners if theirs behaved the same way..as although I liked it..I wasn't sure if it "should" be like that

About a year ago a 1983 Mark IIB in good condition and for a fair price came up for sale(They don't come up all that often in the UK)
It had Reverb and EQ and the EV 12L (still 60 watts)and I thought great...An upgrade with the EQ etc and at least a great spare to have..

This amp could not have sounded any different to my mark 1981 IIB..The clean channel stayed totally clean with volume 1 at 10 but it was a very "sterile" clean and very trebly...almost ice picky?

The presence circuit on mines is fantastic...the range from 0-10 is huge on the '81..Between 0-3 you get a lovely warm tone..
The presence on this one was no where near as effective and I couldn't really dial out the harsh treble...(Only with the EQ)but still had a slightly harsh sound and the lead channel was also no where near as nice sounding as the '81...

I passed on the amp after traveling quite a bit to buy it...I felt bad for the seller but it was a completely different amp...
I thought a Mark IIB was a Mark IIB if anything I thought it would have sounded better..with the EQ etc..I have often wondered if I made a mistake not taking it and if tubes etc might have helped..but yeah it was nowhere near as nice sounding as my '81 model...and didn't have the same feel

Incidentally the treble shift only works on the lead channel on mines too?Is it not the other way around?Is it not the later amps that had the treble shift available on the clean channel too?

Here's the little video I made of my clean channel..I love what it does but I was wondering if it should have had as much gain on the clean channel but other users thought it was just fine?If I want Fender clean I simply have volume 1 at around 5.

Excuse the playing...I'm just sitting messing around. https://www.youtube.com/watch?v=V6xMQY_2Wtc

Just saw your video on Youtube: I think, that amount of gain is quite normal on the clean channel: with the same dialing I get similar crunch with a Les Paul. Sounds great. If you dial in a lot more mids and a bit more bass you can get some nice dumble solo sounds too.

 

[GJgo]

I've had 4 IIC+, and one very late IIB (coli) with the RP9C and Mike B's loop mod. That amp crushes. TBH I like it better than most of my IIC+s, at least with their native power sections. I've never played an older IIB but I know it was a constant evolution.

Here it is solo-
https://youtu.be/tvNVb-llDxk

Here it is in the mix-
https://youtu.be/qeuJroofynU

 

[Firefight]

Progressively every revision tightened the low end until the mighty C+ arrived in all its glory achieving that tight punchy definition and gain needed for any style like no amp prior to its inception.

 

[Rob Lockwood]

I originally posted in 2018 about differences between Mark 2bs. There seemed to be little interest in the subject and after a while I stopped checking in. I've just returned to this post by accident and seen some great replies added a year or so later, so thank you. Its good to confirm that the 1983 mark 2b is very different from the early models. The video posted by MK IIB is really useful - that is the sound that I had heard from a friends 2b years ago and what I wanted (and still do). The clean channel starts to overdrive early and has a lovely slightly compressed sound with a singing mid range focus that I really like and haven't heard from any other Boogie. My 2b could hardly be more different, the clean channel is very clean and has a slightly mid scooped tone that is to me very Fender-like. Its a really great clean tone and I think many clean sound players would prefer it, but just not what I expected and no amount of tweaking settings gets it close to that early 2b sound. I did a small mod to increase the gain and it does now break up a bit at higher gain settings but its a brighter, harsher overdrive, not the same at all. The drive channel is very different too, much more aggressive and crunchy. The explanation that the gain boost function is really the pull deep function from the Mark 2c makes perfect sense. The clean channel of my 2b matches the 2b schematic I found online well, but sounds completely different, I don't think any of the schematics I've found on line can be correct for the 1981 mark 2b. If I could find the real schematic of the 1981 2b that I really like maybe I could mod my 83 2b to be the same?? I'm comfortable with doing the mods If I know what to do . Alternatively I think I need to get hold of an earlier mark 2b which probably means moving on the one I have unfortunately. We will see. Thanks again for the replies!

 

[Wyzard]

I'm sure I've owned, seen or heard of four iterations of MkIIB so far, with preamp boards from 8C (as mentioned above - I've never had one myself), through 9A, then 9B, to 9C. In my experience, these get further away from the big Fenders (and, obviously, the more Fender-esque MkIIA as well) as they evolve. The low-end tightens, and the mids fill out a bit more too. I also prefer the top-end of the earlier IIBs, so there's probably something changing there as well.

For my money, there's definitely a slightly unwelcome change in the lower-mids as this process continues, which sounded/felt to me like a progressively greater overhang; not a big thing, but enough to have me fighting with it. YMMV.

So in the end, this led me to move on my 100W IIBs. Now I just stick with my early Colis, which work for me as the best compromise between MkIIA and IIC+.

 

[Dude2Dude]

Mine is a real early (May, 1980, serial #53xx) fully loaded combo with X100 tranny and RP 8B board. It may have been a stransitional model between the last IIAs and the IIBs — but it definitely has the effects loop, etc.

 

[Red Wood]

Hope it's OK to jump on this thread. I've never worked on a Mesa before but a Mark 2b landed on my bench this week that had died a while back when the owner hit an A/B box to switch his signal from another amp and it died on him suddenly**. I traced the problem to a .047 orange drop cap to ground on the wire between the Standby switch and the choke, but I cannot find this cap in any schematic I'm looking at. Before discovering that cap was a dead short I had already thoroughly evaluated the entire power supply. One diode was suspect with significant reverse leakage current so I changed them all to fresh 1N4007s. The filter caps are mostly original so I'm going to change them but still good enough for bench testing purposes for now until parts arrive.

The other issue I have is just a lot of resistors in the power section don't seem to reflect values I'm seeing in the schematic so I'm wondering if this thing is modified or were there a few different power supplies put out in these amps and they just never published updated schematics? The odd value resistors have appearance consistent with the rest of the amp so I'm guessing if it was modded it was done by the factory. FWIW the 30uF500V caps are original dated 1982 but it appears the pair of 220uF300V reservoir caps are similar Spragues but dated 2005. I'm in NorCal just a few hours from Petaluma so I guess odds are good it could have found its way back to the factory at some point just based on that fact. Just trying to figure out if this is how it left the factory from day 1 or did somebody go nuts in here at some point, and if so, why exactly?

**It's not clear using the A/B box caused the problem, and I actually suspect the Standby switch was involved when this happened. I've read it's a bad idea to place a Standby switch directly in front of a choke, which is exactly where this one is located. I suspect the cap to ground may have been retrofitted to suppress loud popping when taking out of Standby but that's just a theory. I've temporarily replaced that cap with a .047 Mallory I had on hand but think before I return the amp I might stick a larger 0.22 orange drop in there. Please correct me if I'm wrong but seems like this might be a place where bigger is better to prevent the same thing from happening again?