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wanders 31st August 2012 07:10 PM

McIntosh C-24
1 Attachment(s)
This question could probably be posted in several forums, but I'll try here.

I'm looking to replace a semi conductor on my C-24, the first McIntosh solid state preamp. The part is q-18, a NPA 132-014, power regulator transistor. Everything I have on the part is shown on the attachment which was assembled from several sources.

I've found a couple of other queries on this part on other audio boards, but no recommendations. Any help would be appreciated.

FraserSoft 31st August 2012 07:30 PM

1 Attachment(s)
Not sure if this helps but it's a Data sheet on the SE7001 shown on your attachment.

Kindhornman 31st August 2012 08:03 PM

McIntosh schematics are usually pretty good about identifying the standard parts. Do you have a real official schematic. I have the MA6100 which is in the shop, I didn't have an oscilloscope to identify the problem, but I had the schematic and it identified all the parts not just with a part number but the actual values.


Kindhornman 31st August 2012 08:11 PM

Here is a link to the actual schematic. It is a zipped file. download, unzip and take a look. I didn't look hard for your part but it should be there.
McIntosh C24 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics

wanders 31st August 2012 10:48 PM

Thanks for the leads. I do have the service and user manuals which have circuit descriptions, schematics, and part numbers. I tried to include the ps schematic in my attachment, but the up-load load limits caused me to delete it and only inlcude the verbiage. The NPN description and Mac part numbers are from the service manual. The suggested Fairchild replacement info is extracted from a Mac cross reference guide.

The schematic for my model is slightly different than the one shown in Kindhornman's attachment. My q-18 is shown as q-16 and/or q-102 on Kindornman's attachment. The voltages, however, are the same: b=75.9, c=80, e=75.

Kindhornman 2nd September 2012 06:38 PM

If you have the Fairchild part numbers can't you find the replacement parts or an equivalent part? Have you just done a simple Google search for the original part numbers?

wanders 5th September 2012 05:17 PM


Originally Posted by Kindhornman (
If you have the Fairchild part numbers can't you find the replacement parts or an equivalent part? Have you just done a simple Google search for the original part numbers?

I've exhausted all of the search capacity at my disposal. If Google could spit out a current replacement part, or even a set of parts, I would have sourced a bunch and tried 'em out. All of the information I have on the component was listed in the attachment I included in my first post, that was gleaned from a variety of sources. Over the past several years,on the AudioKarma forum, there have been numerous Mac builders who have sought information on replacements for that component, but nobody has yet suggested anything. I've been hoping an engineer might take a look at the schematics and suggest a replacement part. I think FraserSoft's data sheet on the Fairchild part probably contains some insight. I'm going to an audio club meeting tonight; maybe one of those guys can help.

Anyway, all comments and suggestions are gratefully received.

Kindhornman 5th September 2012 05:59 PM

Stupid question but have you contacted McIntosh themselves? Sometimes they are actually helpful. It appears that it shouldn't be that hard a part to substitute another transistor into that position on the power supply. Just put up a question about power supplies in that forum listing with the schematic and show the position that you are trying to replace. I bet you will get more suggestions than you will want.

wanders 6th September 2012 06:06 PM


Originally Posted by Kindhornman (
Stupid question but have you contacted McIntosh themselves? Sometimes they are actually helpful.

The idea is very logical; unfortunately, I've tried it without success. When I first got this preamp, I contacted McIntosh asking about replacement can capacitors (which need attention). They were polite, but said they didn't have any suggestions, but I should try a couple of vintage audio suppliers. They provided a couple of suggested sources. I contacted them, but never heard anything back. The problem with this unit is that it's Mac's first solid preamp and the guys rebuilding these units have focused on the c-28 as the optimum unit to refurbish. There is lot's of information on that unit. I got a good deal on the c-24, but, if I'm honest with myself, I would have been better off paying more and getting a c-28.

I'm going to follow the suggestion to ask for engineering advice on replacing the transistor with one that specs out properly. Thanks.

Kindhornman 6th September 2012 06:21 PM

If I had my manual for my MA6100 I would look at that. I assume since that was the first integrated amp preamp that they are probably similar in construction. But I don't have either the unit in hand or the schematic which is with the unit. I've had it since new and it has a problem that I could not locate as I did not have access to a scope at the time to determine where the signal was getting lost. I also tried to find information on the Fairchild transistors and couldn't find anything. I was very surprised. If someone had an old Fairchild catalog then you could at least get the electrical specs on the transistors but without that I couldn't find a thing.


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