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Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #96213  by JonnyBoy
 Thu Mar 31, 2011 1:02 pm
Cool Tap. This helps get an idea what the parts are that go bad. I wish I saw this months ago, I would have been ahead of the game without having to piece the process together one tidbit of info at a time. I had to beg many kind souls for some info on what to do to fix the same thing.
 #96237  by mijknahs
 Thu Mar 31, 2011 6:20 pm
I've always been told you don't need to replace the filter caps unless they're leaking or there is a lot of noise.

You can replace the smaller electrolytic caps that are soldered on the boards though. They definitely need replacing if original.

Jim
 #96244  by JonnyBoy
 Thu Mar 31, 2011 9:35 pm
To link this discussion to another here is what brad did for MODZ Mc250 to bring it back to snuff.
What I did was leave the two silver smaller can's in place, but inside the amp I disconnected them. The replacement cap's of the same values are SO much smaller than they used to be, so they all fit very nicely inside there. The only trick was the silver can closest to the front of the amp is actually a single and is for the negative supply. That cap's polarity was a bit confusing at first when looking at the amp because the + side goes to ground. Electrolytic polarity is CRITICAL because if you reverse them, they are like a dead short and things can fry real fast. Plus they can pop or at least smoke and ooze some nasty liquid.

Also, the 2 10uF cap's on the input board are for coupling audio, so I used poly film types instead of electrolytic since film is a far superior audio coupler. I didn't quite go to 10uF, but went 2.2uF instead. Still plenty of bandwidth there, and for Jerry style guitar, not an issue at all. I believe that some of the Mac's even used to use 2.2uF there instead of 10uF.

At first Tracy's Mc250 bench tested about 63 watts on one channel and 68 watts on the other. Kind of mushy and sluggish compared to what it should sound like. After this re-cap job, both channels were delivering a solid 82 watts per channel right at clipping. This particular Mc250 of Tracy's was by far the cleanest circuit I've seen in one yet. Outside had some metal pitting, but inside, I swear this amp had never been abused or even opened up before he got his hands on it. Every component was stock, zero charring around the Sentry Monitor resistors as we see in most used Mc250's. This baby came right back to life with tons of clean power. I love these amps.
This was what he did apparently. Hope this info is at home in this thread of how to Repair Macs.
 #96245  by JonnyBoy
 Thu Mar 31, 2011 9:53 pm
I have been having issues now with my MC250. I play low through it and its fine, I start playing at a reasonable volume or pushed it starts going out and making my speaker flop and freak out. I change power amps and it is gone. no issue anywhere else, so it is the MC250. since it is all working, I am assuming it needs cap replacement and upgrading. I will play and things will seem fine, then I dig in and it starts going in and out on me, and making the speakers flutter. I turn down the volume and wait a second I can play and its fine, then add more power again and there it goes again. New caps?


Does anyone know the kind of signs or behaviors the system will have when caps need to be replaced?
 #105517  by Pete B.
 Tue Nov 22, 2011 9:23 am
I now own that MC250 that Brad worked on.
It sounds great!
I play it regularly with one of my Trio's which has recently gone to a 4-piece with the addition of a Bobby guy.
Most recently we jammed last Fri night and Sat afternoon (the Bass player has a nice studio).
I went "Stock Jerry"... I used an Adamas pick, AB763 Volume on 6.9, treble-10, mid 5.5, bass-0, Bright switch off. Mac at about 10'oclock (a relatively low volume jam - the way I like 'em these days).
:cool:
Anyway... sounds exactly like Jerry. :hail:

I haven't watched this vid yet...
The only mod I would like is for the inputs to be permanently converted to 1/4" inputs.
Have any of you guys done that?
 #105520  by waldo041
 Tue Nov 22, 2011 9:30 am
Pete B. wrote:I now own that MC250 that Brad worked on.
It sounds great!
I play it regularly with one of my Trio's which has recently gone to a 4-piece with the addition of a Bobby guy.
Most recently we jammed last Fri night and Sat afternoon (the Bass player has a nice studio).
I went "Stock Jerry"... I used an Adamas pick, AB763 Volume on 6.9, treble-10, mid 5.5, bass-0, Bright switch off. Mac at about 10'oclock (a relatively low volume jam - the way I like 'em these days).
:cool:
Anyway... sounds exactly like Jerry. :hail:

I haven't watched this vid yet...
The only mod I would like is for the inputs to be permanently converted to 1/4" inputs.
Have any of you guys done that?
i am totally stoked to hear your diggin on the equipment tone side of jerrys awesome rig, as i know you already have the chops/fingers. the combo i can only imagine sounds great!

i have an mc2100 i did the 1/4" input jack mod to. it is a very easy mod to do if you have a handle on soldering which is only the input wires and possibly grounds, 4 total. i carefully and slowly drilled out the RCA jacks, and redrilled for the 1/4" jacks after i had removed the RCA's. super easy and should not cost that much if you were to have a shop take care of it.


peace,
waldo
 #105522  by mijknahs
 Tue Nov 22, 2011 9:52 am
Pete B. wrote:The only mod I would like is for the inputs to be permanently converted to 1/4" inputs.
Have any of you guys done that?
I've done that to my MC100 recently and also to my MC2300 a while ago. So much more convenient. I hate RCA jacks.
 #105573  by JonnyBoy
 Wed Nov 23, 2011 5:20 pm
I went to radio shack and bought a 1/4" to RCA cord to go from my SMS to my MC100. It works great. I changed my 250 and 50 to 1/4", but kept the 100 stock in case I sell it I guess (yhea right). I have broken 3 of those cords on the 100 so far, and one of those times the pin in the middle broke off in it and got stuck into the Mac end of the jack. It has enough room to push it all the way in, I guess you get one Gimme before your screwed and have to change the RCA plug out anyway. There is really no "sound" difference in using RCA or 1/4", just the ease of not needing a special cord.

I love my rig above and beyond many many different amps/rigs I have used. Anyone on the fence wanting to get one or think it makes little difference, I strongly urge them to give it a go. I think its about one of the only rigs you can sell off for close to what you paid for it in the end anyway. Not only Jerry lives in there, but many great tones. on the "Con" side of the coin, it is a bitch to move around. get wheels.