McIntosh - Hints and Kinks

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When working with the turret boards in classic McIntosh amplifiers, be sure to mount new parts (usually resistors) to the same specs as McIntosh engineers did.

A sturdy mechanical connection of a part ensures are secure and conductive solder joint later. It's not hard to do, looks neat and is superior in function.

A Soldapullt does a nice job removing excess solder from a joint so that the original part can be unwound from it's post.

110CLsAKysL._SL500_AA300_.jpg
 
I don't mind helping out as long as I have time, just don't bite off more than you can handle. Good soldering practices and neat workmanship count with McIntosh, they were works of art when new, lets keep them that way.
Nice "how not to" photo's. :thumbsdn:
 
What kind of modifacations are members looking for....future serviceability....added reliability......."sound"?
 
I don't mind helping out as long as I have time, just don't bite off more than you can handle. Good soldering practices and neat workmanship count with McIntosh, they were works of art when new, lets keep them that way.

On a side note...where did you get the squirrel mugshot mug (2nd pic, next to cordless drill)?? My wife would love it!!
 
MR67 Mod

There is a published modification for the MR67 and other tuners. It involves placing a .0015 and a 27K ohm resistor in parallel from pin 8 of one 8BL8 to pin 8 of the other 6BL8. This is NOT a slap it in and go modification. The tuner must be adjusted for maximum separation after installation. For full details see Service Bulletin #114 in the document at http://rich.homeunix.com/McIntosh/servics_bulletins.pdf It does really improve the stereo imaging.
 
Thanks for the good read.....have not reread those old 60s service bullitens in years. I find it most interesting the hand holding Mac is doing "warming " all the tube techs to solid state!
 
well I think the "mods" would be good for things like discontinued parts ( I guess that would fall under "replacements" not mods) but thats sort of what we would need to have done. Need to keep those audio classics running.
 
A little story about non-documented mods...

When I was a senior in college in 1968 (I was an EE student at the U of Ill), I had a summer job at Stewart-Warner Electronics in Chicago aligning modules used in APN-159 radar altimeters used in F-4 Phantom jets in Viet Nam. There were four techs who did most of the final tests and alignments and they knew the units inside and out. Every once and a great while a unit would come on their bench that would not fall in spec for one parameter no matter how much tweaking was attempted. They did know from experience that if they changed one resistor from X ohms to Y ohms it would pass.

The unit would go in the field and work fine for many months until a random component would fail. A military tech would go through the unit and find the bad component but then....comparing the schematic to the unit see that one resistor was incorrect. Feeling like a crime solving detective, he would change the resistor back to the value shown in the schematic. Before it could be returned to service the unit had to pass the complete list of tests. Guess what, the unit would never fall in spec for one of the parameters and had to get sent back to the states for higher level testing at the factory. :nono:
 
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Speaker relay for MC2200 and MC2205

There was another thread regarding this but I will repeat it here.

A Potter & Brumfield KUP-14D15-48 relay works perfectly as a replacement for the original speaker relay in MC2200 and MC2205 amps. It is the same product family as the original and is the same size and pin-out arrangement on the bottom. This relay is 3P-DT whereas the original is 3P-ST so there are an extra row of contacts across the top that can just be ignored. Also the Mcintosh relay uses a different version of the clear plastic cover with two mounting studs molded in. This KUP-14D15-48 relay cover does not have studs. Just carefully remove the covers from the old and new relays and swap them.

This relay is available off the shelf from Mouser for about $15 plus S/H. They only had about 10 in stock last time I looked.

http://www.mouser.com/ProductDetail...mraksZquSKhHKYeYqeev6ABM%2b7HDM4HV/xM3yCFmA==
 
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There was another thread regarding this but I will repeat it here.

A Potter & Brumfield KUP-14D15-48 relay works perfectly as a replacement for the original speaker relay in MC2200 and MC2205 amps. It is the same product family as the original and is the same size and pin-out arrangement on the bottom. This relay is 3P-DT whereas the original is 3P-ST so there are an extra row of contacts across the top that can just be ignored. Also the Mcintosh relay uses a different version of the clear plastic cover with two mounting studs molded in. This KUP-14D15-48 relay cover does not have studs. Just carefully remove the covers from the old and new relays and swap them.

This relay is available off the shelf from Mouser for about $15 plus S/H. They only had about 10 in stock last time I looked.

http://www.mouser.com/ProductDetail...mraksZquSKhHKYeYqeev6ABM%2b7HDM4HV/xM3yCFmA==

Absolutely, I have done this, I bought 2 while I was at it.........it is the perfect solution....:thmbsp:
 
On a side note...where did you get the squirrel mugshot mug (2nd pic, next to cordless drill)?? My wife would love it!!

I have that same Mug!

A relic of the epic 2004 Christmas Battle of Ludlow Vt with the chase of a flying squirrel at a ski-house we stayed at. My Sister-in Law called the local cops to chase down the varmint, we caught it and tossed it outside before they could muster the SWAT team.

Many gag gifts were bought, the joke wore thin quickly, so I never gave them the mug.
 
Got to have an appropriate mug for the bench, just like a good temperature controlled iron, and a Variac.
 

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Audio shops back in the day ran on coffee...still have my 3 mast sailing ship mug from back in 1978 right here today.

However this thread is about McIntosh updates and mods so......

Terry,

Back a number of months ago you posted a pdf of a noise spectrum of a C28. I find this interesting and informative. Only 24 times did anyone bother to look at it. It is a shame because it shows how much can be done to improve the C28 preamp.

I have reposted because I believe we all can learn much from it if we bother to study it.

Can you highlight the test equipment you used for those of us still stuck in back in the day?

Do you remember what you did to this unit?

The 60 Hz noise still seems high...I have found shield issues on my project C28, mostly in the filter circuits and the convoluted ground drains....how about you.
 

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Looks like no one is interested in this sticky beyond coffee mugs.

Anyone have an opiniun/experience with the Rightmark analyser program?
 
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The noise measurements were made using Right Mark Audio Analyzer and a Delta 66 sound card with the Omni IO interface in my computer. I have since changed to a newer computer and am in the process of tweaking a new sound board with interface to get reliable data, currently I can loop back on the Xonar Essence STX board and get a base line of 102dB for my SNR. This number is acceptable though I think it can be improved closer to the board specs of 124dB by tweaking the interface.
 
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