MC 250....Now what do I do?

MC 250....Now what do I do?

Postby Stella Bloo » Wed Oct 09, 2013 2:28 pm

Sorry,

Going to sound very stupid, but I just scored an MC 250, it's on its way and have some questions.

FYI, I will only be using one side (50 watts) as I just jam in my home studio. I assume I can save the other as a backup should one side go down?

1. I'd like to have it checked over by a professional and have 1/4" inputs and speaker outputs added so I can plug right in. Any idea's who can do that for me? I am in southwest Florida.
2. Until then, how the heck do I hook up everything. I assume my SMS goes into the RCA input on the front (How do I get a cord for that?) and I somehow have to cut the 1/4" jack off my speaker cable and wire it to the clips? I need a 4 ohm load for my 2X10 K110's?

Any help would be greatly appreciated.
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Re: MC 250....Now what do I do?

Postby tcsned » Wed Oct 09, 2013 3:00 pm

First, 50w is more than enough. Use the other side as a backup or bridge them if you feel like you need the extra power, but it doubt that.

Cables, you should be able to find a decent RCA to 1/4" cable at Radio Shack.

I cut the 1/4" end off a speaker cable and wired it to the speaker terminals. They make a banana plug adapter for the Mac that attaches to the speaker terminals, I have them but have been to lazy to getting around to using them.

Crank it up and enjoy!
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Re: MC 250....Now what do I do?

Postby jenkins » Thu Oct 10, 2013 9:24 pm

You can get quality 1/4" to RCA cables online, that's what i still use after 5 years of having my macs, mine is rack mounted & stays plugged in anyways but unless you have touring to do the 1/4" conversion prolly ain't worth it, I don't really see a need for it. When I first got mine I went to radio shackto get a cheap one to use temporarily & it sounded just fine.

As for the speaker terminals you can order banana clip adapters on eBay & they work great. You screw them on to the speaker terminal and plug in your 1/4" to banana clip cable that you can buy at any well stocked music store. If I played a lot more shows i would maybe go for this mod but playing a few gigs a month like I do I've never really felt it to be that necessary of a mod. Also after getting a Mac it sounds so dank that I haven't wanted to play a show without it so I've never wanted to send it out for that mod. Cool mod but def not needed if you're just gonna Have it hooked up in your studio.

That's badass you got a Mac on the way, be prepared for some seriously great tone, they're the best by a long shot IMHO.
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Re: MC 250....Now what do I do?

Postby JustinJohn » Fri Oct 11, 2013 3:12 am

Don't mod it...

I used to think the same way - get 1/4" plugs put in rather than the standard rca's, and also a speaker-out jack (1/4")... but the gearhead who looked mine over for me talked me out of it. and I'm glad he did. He built a simple 2-prong speaker cable adapter that works fine (and I lug mine around all over town several times a month), and a simple 1/4" > rca cable works just fine from my pre.

=)
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Re: MC 250....Now what do I do?

Postby strumminsix » Fri Oct 11, 2013 7:23 am

Dude, check out this link:
http://www.sweetwater.com/shop/cables/finder.php

I use Sweetwater all the time. Almost always get prices under list and it arrives in a day or 2.
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Re: MC 250....Now what do I do?

Postby SarnoMusicSolutions » Sun Oct 13, 2013 8:48 am

... and it's just like any other day that's ever been...
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Re: MC 250....Now what do I do?

Postby Jon S. » Sun Oct 13, 2013 11:10 am

I not only don't regret a single of my mods, I LOVE 'em. I'm a guitarist, not an audiophile. Well worth every penny. :smile:

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Re: MC 250....Now what do I do?

Postby Smolder » Sun Oct 13, 2013 12:41 pm

I'm in the same camp as Jon here. It's gotta be functional first. Three prong grounded cord (mine is hardwired unlike Jon's, but if I did it again, that would be the way). A power switch... I use a power strip, but it's helpful to power up the preamp before turning on the power amp. Otherwise you can get some very odd noise. A quarter inch jack requires a slightly larger hole that the RCA... and lastly, I put a regular quarter inch jack for the 8 ohm tap. No regrets.
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Re: MC 250....Now what do I do?

Postby tcsned » Sun Oct 13, 2013 1:57 pm

If you're concerned about resale value . . . other than to one of us, the mods don't make sense. If you are keeping this for the long haul, why not have it set up for your use? My first MC2100 blew up during a gig and I picked up a second that's in a whole lot better cosmetic shape than my first. I'm probably going to have it modded with 1/4" speaker outs and line ins, it already has a grounded plug.
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Re: MC 250....Now what do I do?

Postby RiseandFall » Mon Oct 14, 2013 5:53 am

Not to sidetrack this, but I picked up a MC50 a while back. It sounds great to my ear, but as I have nothing to compare it to as a point of reference, I wonder if it could be even better. It is after all a 40 year old amp.
Were I to take it in to get it serviced, what should I tell the repair person to use to get it in original (or better/more Jerry like) condition? Are there preferred parts, or replacement parts I should tell him not to use?
I'm not concerned about the speaker connections or inputs....just the guts.
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Re: MC 250....Now what do I do?

Postby Smolder » Mon Oct 14, 2013 6:49 am

RiseandFall wrote:Not to sidetrack this, but I picked up a MC50 a while back. It sounds great to my ear, but as I have nothing to compare it to as a point of reference, I wonder if it could be even better. It is after all a 40 year old amp.
Were I to take it in to get it serviced, what should I tell the repair person to use to get it in original (or better/more Jerry like) condition? Are there preferred parts, or replacement parts I should tell him not to use?
I'm not concerned about the speaker connections or inputs....just the guts.



When I did mine I went through and checked resistors to see if they within 10% of the value (they sometimes drift). I change all of the electrolytic caps (not all of the capacitors are electrolytic) inside the amp as they tend to dry and leak over time. I did not mess with the large canisters as they showed no signs of wear and are more stable. I also replaced the transistors as they tend not to be reliable if they are original... it was difficult to track a couple of them down as the numbers, codes, and manufacturers have changed over the years. There are several threads with solid recommendation for guys that work on these old macs.
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Re: MC 250....Now what do I do?

Postby RiseandFall » Mon Oct 14, 2013 6:56 am

When I did mine I went through and checked resistors to see if they within 10% of the value (they sometimes drift). I change all of the electrolytic caps (not all of the capacitors are electrolytic) inside the amp as they tend to dry and leak over time. I did not mess with the large canisters as they showed no signs of wear and are more stable. I also replaced the transistors as they tend not to be reliable if they are original... it was difficult to track a couple of them down as the numbers, codes, and manufacturers have changed over the years. There are several threads with solid recommendation for guys that work on these old macs.


Thanks much. I will research the threads (what I should have done to start with).
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Re: MC 250....Now what do I do?

Postby Stella Bloo » Mon Oct 14, 2013 2:15 pm

Thanks for all the help, what about wiring the spekers to the terminals. I currently have a HT 2X10 with JBL K110's and I have a 4 ohm load. Currently using a 1/4 inch on both ends. I assume, I simply cut off one end? Which wires go where and do I need to reverse anything due to the JBL's? I certainly don't want to blow anything!
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Re: MC 250....Now what do I do?

Postby waldo041 » Mon Oct 14, 2013 4:20 pm

Smolder wrote:When I did mine I went through and checked resistors to see if they within 10% of the value (they sometimes drift). I change all of the electrolytic caps (not all of the capacitors are electrolytic) inside the amp as they tend to dry and leak over time. I did not mess with the large canisters as they showed no signs of wear and are more stable. I also replaced the transistors as they tend not to be reliable if they are original... it was difficult to track a couple of them down as the numbers, codes, and manufacturers have changed over the years. There are several threads with solid recommendation for guys that work on these old macs.


If anyone has there mac serviced or is doing the service themselves, I would love to get your used 132-070 output transistors if you are not going to use them in your upgrade. Please have your tech return them to you to give to me!

~waldo
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Re: MC 250....Now what do I do?

Postby tatittle » Tue Oct 15, 2013 6:27 pm

Re: speaker connections

In general, TIP = positive ; RING/SHAFT = ground/return/negative

vintage JBL's are the reverse color code of typical speakers, so Black equals input and RED post is ground. A good way to test an unknown speaker or wires is to touch the 1/4 cable (or the bare wires) to the terminals of a 9V battery (and remove immediately--the speaker will stay flexed as long as both connections are made). This should cause the speaker to flex. Proper polarity makes the speaker jump outward, reversed it will move backwards. I dont think it is particularly harmful to hook up speakers "backwards", but it will give a thin sound as it is pushing air behind the speaker rather than forward into the room.
Last edited by tatittle on Wed Oct 16, 2013 5:31 pm, edited 1 time in total.
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