Fixing/modding/making better my MKIII simul combo need help

[okgb]

To me it has never sounded great , a dry midrange feel , so
now with it's age i'll look at replacing the pwr supply caps
[ although it doesn't really hum much ] and will plan a few mods
to do to it at the same time so trying to plan them together

ser # 16696 appears to be no stripe , rythym 2 is screened over the mkII panel

bought it new mid 80's ,[ with the hype " Boogies retain their value " yeah right ]
the outside pair output tubes are wired triode , i added
[ 1k ? ] resisters between the plate and screen as per mesa recomendation
and mostly i prefer to run el 34's in outside sockets by themselves [ nicer 17 watts ]
added trimmer to control R2 [ changes depending overall master volume ]

It's a bit ratty sounding for overdrive these days , hadn't used it for a while
I would prefer a smoother sound with " texture " not so hard sounding
overdrive decay on the lead channel drops off a little too quickly leaving

Any recomendations appreciated , tia

 

[okgb]

I know it'd be a big job but a sticky with common mkIII
fixes & tricks would be a good idea [ or have i missed it ? ]

thanks again , regards Greg

 

[ltd2recto]

The c30 mod smooths out the lead channel. The C516 mod gives the presence knob more range.

Also good tubes if you haven't already. Tungsram & RFT preamp tubes can be found online for cheap. You cant go wrong with Winged c's in the power amp.

Do you have the GEQ?

 

[kdorsey]

That's a pretty early model and this is where it would be beneficial to hear from the factory on a suggestion. As these MkIIIs start to age to the point where electrolytic caps are drying up and need major overhauls, what would they do if the amp were in their shop? Are add-ons and circuit tweaks a reasonable solution or is this only delaying the inevitable?

 

[Restless Rocks]

Your "no stripe" may very well have the 105 power transformer left over from the MkIIC+ production. Very few people also seem to know that the no stripes have a different circuit board than all the later mkIII stripes. The R2 circuit in the no stripe is as it is on available mkIII schematic. The purple stripe and forward used a new board with a redesigned R2 circuit. These particular no stripes make outstanding candidates for the "III+" mods (these are a few tweaks to make it sound much closer to the IIC+). And yes new tubes will bring the amp into new territory. These are very good sounding amps.

 

[aaronlyon]

Just in case you didn't already: Run it thru different cabs to see if a speaker swap would please you.

 

[okgb]

Thanks for the replies so far
I'd sold my Marshall w412 in the 80's cause
it was hard getting help with hauling it and got the mkIII
which seemed amazing at the time to not need o/d pedals
eveything sounds better through 4x12's to me , i'd swaped
the original mesa speaker for their celestion model .
Not crazy about the 5881 in the outputs , the best "era " of 6l6's
were the green printed U.S. ones from the 80's [ as i recall ]

mine has the eq , which i would leave in to compensate for the rythym 2
sound [ although these days , i could easily not use the R2 ]

Other than the effort can't see changing the psu caps hurting but
it's the shipping from Canada to petaluma that i'm hestitant about
[ money vs results ]

 

[ltd2recto]

If you're not getting alot of hum, changing the caps will be more preventative maintenance then anything. Re-tubing &/or a speaker swap will give you better results for the $.

I have the EVM12-L & it's a great speaker. Thought it sounded better then through my marshall 1960av w/ 4 v30's. Although I didn't tweak it much with the 4x12.

I'm not even gonna lie. My 750 slider lurks anywhere from 65-75% of the way down for all channels (I only use rhy1 & lead). Just to the point where its not so in your face. That being said I play metal but it sounds great with the clean channel too IMO. Lately I've been pulling everything except the bass knob (humbucker guitar, I pull that too when using my strat). When you do that & run the presence higher it sounds killer.

You could spend about $100 & get 2 used tungrams (v1-2) & 1 used RFT (v3). This is a proven combo in the preamp. What tubes you got right now? And how old are they?

What kinda sound you goin for anyway? Its possible you're just looking for something different & no amount of $ in the amp will get you where you wanna go.

 

[okgb]

Since it'd be a big loss to sell it having bought new , at
the very least it's a great 17watt pwr amp [ outside el 34's ]

Having not played it much in the last decade i remember it sounding better , so
Smoother [ i will do the cap changes ] and having a " loud amp sound " [ slightly dirty ? ]
are the goals , right now the lead channel decays too quickly [ and in an ugly way ]
but all of the tubes are boogie stamped , some replacements over the years
I have some telefunkens for possible trade ?

The last version of 6l6 that sounded good [ that i have left ] is a
U.S. Syvania double getter [ i have some singles as well ? ]
green printed str 387

Doesn't seem to have the 105 xfmr , and i can see that from calls to them in the 80's
i'd already changed c27 [ looks like i added another 10pf in paralell ] and
changed c214 to a .22 [ to lessen the mids on R2 ? ]

the pcb is marked MESSA-BOOGIE CP1E C1984

the psu caps don't look hard to change , just have to find a place to get
decent axial types

anyone know the value for the R2 pot ?
anyone have a clean [ not copied 100x mkIII schematic ? ]

thanks again everyone , regards Greg

 

[chipaudette]

The comment "decays too quickly" sounds like the amp has a problem. Is there a store around with a Mark III or Mark IV? Compare the sound of your amp to either one of those. Is it tremendously different or basically the same? If it is really different, you've got a broken amp. Most likely a dead relay/LDR.

A trip to Mesa is expensive, but usually worth it. It's going to get done right. You might have some explaining to do about all the mods, though. That'll make their life much more difficult.

Chip

 

[okgb]

Any mods were done after talking with them [ albeit some time ago ]
for it's value , doesn't seem justified to send it back
will order caps and play with what preamp tubes i have [ nos U.S. ]
that seems the course of action
caps , tubes , and speaker