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Restoration Process: MC-40
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MC 40 Complete Restoration

The MC 40 is one of a series of mono amplifiers produced and sold by McIntosh Laboratories. Back in the day, when things were mono... you only needed one. No problem, for stereo, simply get two of them, use a stereo preamp, and there you are. These are particularly wonderful amplifiers. They have a very good sound, very smooth and very warm. They are quite simply designed and very well constructed. The tube complement is not at all exotic, so you will never have any trouble finding tubes for it. They are not very full of surprises. The work that they require is very consistent, making it easy to predict what will be found when you get into one. There isn't a whole lot of need in this write-up for me to tell you how to evaluate whether yours should receive a restoration or not. In fact, there are only two types of MC 40's: those which have recently been completely restored, and those which need it. Note that hiring some clown to replace two or three caps and leave the rest is no overhaul. Capacitors do not after all enjoy being 40 years old. They become cranky and disagreeable and forget who they are, they become paranoid and think that the electrons are out to get them. So don't sweat checking it out yourself. If you have just purchased an MC 40, send it in. If you found one in the closet, send it in. If Uncle Otis gives you one, send it in. If you have been using one (two) for a while and you do not wish to walk in and find that one of the priceless transformers has been damaged because of a stupid bad capacitor... you have it... SEND IT IN!!!!! Hmmm, I wonder if I made that point with sufficient emphasis.

In all seriousness, this is extremely important because the only parts that are nearly impossible to replace are the transformers. Since a cranky capacitor can destroy these priceless transformers, a thorough restoration is the only way to go.

all ready for action

Since I have now convinced you that you benefit greatly from buying the complete restoration for your MC 40, you are undoubtedly champing at the bit to find out what that consists of. You already know that capacitor replacement is the name of the game. So you may find yourself thinking that it is simply out with the old capacitors and in with the new. Furthermore, you may think anyone can do it, so you don't need a wise acre like me to do it... right? Wrong! This would fall into the category of "don't try this at home". Here is the deal: in the power supply, you will find rather large can caps mounted horizontally. One of them has three different taps, and the other two are one each. Those particular caps as unavailable as it gets... you absolutely cannot get them. So what to do? The solution is relatively straightforward. Caps of the same value must be found and then they must be mounted in some very tidy way so that all of the electrical connections which were present in the original design and set up are duplicated. Caps of the proper values can be found. In amps of this sort, they are usually not extremely high in their capacity or mfd values, but they are often up in the 500 volt range. No problem, in fact new caps are usually smaller in size which is very helpful when it comes to the mounting question.

from above

The preceding picture will give you a sense of what you are up against on the cap replacement front. All of the caps removed from this MC 40 are laid out in front of it. As you can see, some of them are fairly large. The filter caps from the power supply are the largest ones. These were mounted on a bracket under the chassis. Since new caps will be physically very different, the same mounting is impossible. I chose to locate caps of the appropriate value and to epoxy them in. The original bracket was a perfectly fine place to put them. So check it out:

And here they are, folks.

In the preceding picture, you can see the bracket on which the original cans were mounted. This bracket was the obvious place to epoxy in the new caps. It was actually a very good point to run various ground connections. After all, in the original design, many grounds went to the negative lugs of the cans, and these were mounted in the bracket. It struck me that using this bracket for the grounds was in keeping with the spirit of the original design. So, simply put, the key to a successful repair of a piece like this one is to locate the new caps in a very stable place, and then to wire in all of the original connections. It isn't rocket science, but you have to be very deliberate and precise. The mark of doing it well is in the testing. If, after several hours of wiring, you can plug it in and it works on the first try, no corrections required, then the job has been well done. To the left of the bracket and the new filter caps, you will see the pc board which holds all of the coupling caps. These are replaced as a group. After this has been accomplished, the unit will have no original capacitors in the circuit at all. After this has been done, it is necessary to remove the selenium rectifier and replace it with a silicon diode.

for a good time, call (512) 294-5635

I have so far not mentioned the tubes. Of course the tubes get checked during this process. If you have early or original tubes in the unit, they may still be good. They were rather well made so they are worth using if they still test well. If not, or if you wish to upgrade, there are a world of tubes out there to choose from. Once the unit has been recapped, it needs finally to be cleaned up, both cosmetically, and the tube sockets should be cleaned with a solvent, and then be deoxidized. After that is done, the unit needs only to be checked for proper performance and set up. At that point, it is ready for additional years of service as a very sweet and beautiful performer. Enjoy!

a parting glance at all of those lovely caps.

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