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Learning about this stuff! I have newly acquired gear, and some questions.
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Old 12th November 2008, 06:09 PM   #1
Scottoberfest is offline Scottoberfest  United States
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Join Date: Nov 2008
Default Learning about this stuff! I have newly acquired gear, and some questions.

Hey guys,

I am a recent grad...and although I am a musician, I have very limited experience with vintage audio gear. Any help is appreciated.

My aunt just gave me her old stereo system from the 70s (she knows I love this stuff). I now have a McIntosh Mc2105 amp, Forte preamp, McIntosh Am/Fm Tuner.

I also have her speakers which are particularly interesting. They are two large GNP cabinet speakers. After some research I found that GNP was a custom speaker builder in Pasadena, CA. It was started by a CalTech grad who had a unique speaker design. My aunt says these things were a few thousand dollars when she bought them.

My room is completely taken over by this stuff right now, and I have everything powered up. It sounds incredible.


I have the speakers wired to the 8ohm connector on the 2105. Is that correct? I can't find information on the speakers to figure out what their preferred impedance.

What kind of speaker wire do you recommend for this system?

Anything I can do as far as maintenance on the amp? Cleaning? Replacing parts?

Thank you!

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Old 12th November 2008, 08:32 PM   #2
collumbo is offline collumbo  Germany
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Join Date: Feb 2007
Location: neustadt
Hallo Scottoberfest,

have u tred the contact at


to get infos; i hope it helps...

only cleanig these exquiste components and enjoy their sound... ;-))

best regards
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Old 13th November 2008, 09:39 AM   #3
djk is offline djk
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Join Date: Feb 2001
Location: USA
Try the speakers on both the 4R and 8R tap, see which sounds the best.

You can't hurt it either way.

If you like the amp and want it to run forever, replace all the caps, they're dried up.

I own a MC2100 and two MC2120s.

Caps wear out.

Even when not in use.

This list is for the MC2100, electrically it is the same as the MC2105, just without the meters.

Even though your old amp is still working, you have no idea how much of the music you are missing.

The parts are inexpensive.

Digi-Key is good, Mouser has no minimum order.

Posted by djk (M) on July 11, 2004 at 04:29:36
In Reply to: Re: MC2105 @ $ 100 even @ 20 yrs old is a best buy for me. posted by julian4@telkomsa.net on July 06, 2004 at 14:58:04:

The sound would benefit greatly from replacing a few dried out electrolytics, and adding a few film types here and there.
C301, 302 is the main input coupling cap. It is a Mylar type so it is likely to be OK, upgrading it to a Polypropylene type with give a smoother sound to the high end (0.47F).

C307, 308 are emitter bypass caps, 100F 15V. Replace with same type and add a 0.1F film bypass.

C309, 310 are the output coupling caps for the pre-driver section, 10F 25V. While a film type would be better, size is a problem. The DC bias across this cap also helps out with its being an electrolytic. Replace with same type and add a 0.1F film bypass.

C303, 304 are the DC power supply caps for the front end, 470F at 25V. Replace with same type and add a 0.1F film bypass.

C1, 2 are the feedback loop caps, 330F at 3V. The signal goes through these so replacing these with new ones and adding a 0.1F film bypass really opens up the sound. Go with as high a voltage as what space permits.

C11, 12 are the DC supply caps for the voltage gain stage, 150F at 50V. Replace with same type and add a 0.1F film bypass.

C201, 202 are the main filter caps, 39,000F at 40V. These may be quite expensive new, although I have seen them surplus for very low prices. I would use then unless signs of leakage or amplifier hum are there. Add a 47F at 50V cap in parallel with each.

C203 is a multi-section cap that will be very hard to find a fresh date code. New caps are small enough that they may be wired to the terminals of the old one, leaving the old one in place. This cap is important as it provides the current for the diff pairs and the VAS. The sections go 80/80/150/50F with the voltages being 200/200/150/150V. If you measure the voltages 100/95/90/80V are typical, so 200V caps are not really needed, but 100V is not enough.
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