COMPLETE RESTORATION SERVICE---MCINTOSH MC-240

MUST READ---MUST READ---MUST READ!!!!!NOTICE: You are reading a listing for the service required to make the McIntosh MC-240 work well in spite of its age. If you have an MC-240, you should have this work done, so read on. If you are thinking about buying one, it will come with all of these old capacitors. Ignore the fellow telling you that it works well (though it may). You still need to have it restored, so read on. If you simply are interested in what sort of wild story I will come up with on this occasion......read on.

You have probably bought into the line that McIntosh tube amplifiers were designed and built in New York. Well, actually they were built in New York, but the original design is much older, and not many people know this. The space aliens who came to earth long ago and taught the Egyptians how to build the pyramids also brought the design for these tube amplifiers. Now at this time in history, there was no rock and roll, and no jazz either, Mozart was chronologically a fair ways down the road, so the Egyptians didn't really quite know what to do with it. So the design languished until Mr. McIntosh, on a secret trip to Egypt, found the schematic and put them into production. The MC-240 is a wonderful piece that easily lives up to its heritage. In view of their considerable value, they demand premium restoration at this time.

Besides very excellent performance, these amplifiers are very stable and very reliable. The entire tube complement can be replaced as they are common types. The transformers are almost never bad. The capacitors though are now pushing forty years or so. This is a long time for capacitors or for primitive hunter-gatherers so it is very necessary to replace every damn one of them. The filter capacitors are especially important. They can, without warning, go defective and draw a lot of current through your precious and irreplacable transformers and eat them. Just like that.....bad idea. The coupling caps are not likely to create dramatic failures, but they are also way too old, so out they go. Considering that capacitor technology has come a long way since the 60's, you can expect really good results. This is one of those cases where "better than new" is possible. The amplifier in the pictures received Nichicon electrolytic caps and those big fat Mallory tubulars for coupling.

Doing the "clean sweep" on these guys is the only way to go. Often, these will come in and they will have been repaired several times over the years. There will be a mishmash of coupling caps, various brands and questionable quality. It is also not unusual to find that the work done on them was a little haphazard as well. Replacing everything makes it possible to clean up any funk and to make it all pretty. If somebody pull off the bottom of the unit to simply gaze on the work, you want them to say "Gee, that looks nice. The amp in the pictures is a fine example of the end results. If it looks great, it will sound great.

I am not big on changing out the terminals. I think it has less value if it is modified. I suppose I have seen too many ham handed terminal replacements. The RCA jacks are way permanent in the panel and they work well after being shined up. The barrier strips are just fine for speaker wire if you get some nifty small size gold spade lugs to go under those screws. Usually the tube sockets are just fine after they have been cleaned and deoxidized. Normal cosmetic must be done carefully! You want the chrome to shine and you want the lettering to be all there. If you have a "cosmetically challenged" piece, there are folks out there who do physical restorations. The thought scares me though. I saw a re-chromed one on eBay once that looked really sloppy. Even rusty ones can be cleaned up quite a bit.

The following text is meant for those of you who are interested in a detailed description of what is done to one of these amplifiers......what exactly is a "complete restoration" anyway? So for the technically minded, very interested, or just plain geeky, read on. Bear in mind as you read this that I am not recommending that you perform any of these procedures yourself. Quite the contrary. If you are not a trained technician, then stay the hell out of there. The 400 plus volts at the power supply is quite dangerous so DON'T DO IT. This information is here only to give you an idea what goes on when this sort of work is done. Please note also that the complete restoration for, say an MC-240, is pretty similar to what is done for an MC-75 or one of the others. The practical restoration is much the same with the variations being that some models use solid rectifiers, some use tube rectifiers, different models use different output tubes, you have mono amps and stereo amps, etc. Additionally there are layout variations and it is important to bear in mind that since most of the McIntosh amps were produced over a period of years, they are not all the same. My personal MC-30's are different from each other in board layout and other ways, but they look the same from the outside, and sound the same.

The very first step in restoration is to establish your starting point. These amplifiers frequently come to me after having been stored for a good while, so do we just plug it in and see what is up? Not at all....that would be DUMB, so you shouldn't do it either. In fact let me say right here, if you have just acquired one of these, or have just taken yours off the shelf where it has languished now for 15 years.....DON'T PLUG IT IN!!! Here is the right way to do it. The first thing I do is to check the tubes to make sure they are ok. The tubes that came with these were very good, so they are often ok. Once the tubes are confirmed ok, the unit is hooked to an eight ohm load, either speakers or load resistors. It is then plugged into a variac (variable line transformer) with an ammeter on it. A variac gives you the ability to introduce the amplifier slowly to operating line voltage (ac 117) while monitoring current flow. If it draws too much current during the test, then something is wrong and you congratulate yourself for avoiding the fireworks that would have resulted had you just plugged it in. I like to run it up to about 30 volts and confirm that the ammeter moves very little. After a while, I will run it up to 60 and confirm the same thing. If the current flow is as it should be, you can then run it up to the full 117 volts. This must still be done carefully though as exciting failures are still possible. The next step is to confirm that the tubes light up properly, and that it plays somewhat. Any sound at this stage is satisfactory as it confirms that it is mostly intact. Remember that at this point in the process, you never leave it turned on and leave the room....it is still too dangerous. So now we check the power supply voltages against the values in the manual and if they are within 10% we move on. Next, we check the bias on the output tubes. The service manual will indicate what the bias voltage should be and on which pin.....it varies according to the output tube used. If it is pretty close, and if none of the outputs glow too brightly, we move on. Finally, we wish to have a feel for the function of the output tubes are in a dynamic environment. This is accomplished by measuring the plate current of the outputs. This is measured in milliamps, and is confirmed against what the RCA tube manual specifies for the output tube in your amp. At this point in the process, a 20% or even a 30% variation in the plate current from one tube to another is ok. It just has to be in a sensible range. Now you have established that the unit is unlikely to catch on fire, and that the transformers are functioning correctly.

We are now able to begin the restoration process. We know the condition of the piece we are working on. Nonetheless, I like to add one additional check just for the fun of it. Of course we can now turn it up a bit and see how it sounds. Since we have the load resistors handy, why not check to see how close it gets to its rated power and distortion. It is a relatively simple process. We run a sine wave into it, at perhaps 400 hz or 1000 hz and run it up until it clips. If the unit is close to rated performance, the wave will be well shaped and precise, and it will clip the top and bottom rather cleanly. You won't get a crossover notch unless you really get on it. McIntosh manuals will specify the power output of the various amplifiers through an eight ohm load, but they always beat that, especially at 400 hz. At this point in the process though don't expect a lot. What you will probably get is a weaselly looking wave that gets even weirder as you turn it up. It surely won't sound good when the wave looks like this, and it is unlikely to reach rated power. It is not unusual for the unit to clip at 10 watts or less. Don't worry about trouble-shooting the unit for this obvious performance failure. Usually, once it is recapped, all of this trouble goes away. If it is still sub-par, then you can get serious with it to locate and remedy remaining problems.

So now it is time to begin the serious part of the job. All McIntosh amplifiers have a circuit board running the length of the unit under the tube sockets. It will have resistors populating one side of the board and capacitors on the other. Some of the caps are black with writing on them, and others are identified by their color code. All of these caps must be replaced as they have significantly changed value over time. Since new replacements of the original caps are no longer available, the technician gets to decide what new capacitors are most suitable to the unit now. I have been installing Mallory tubulars for a while now, and customer reaction suggests that this is a good choice. There are many other options though, from relatively inexpensive off-the-shelf caps to the very fancy and esoteric. The most premium of these cost a great deal of money, and those who sell and advocate them will tell you that they make a world of difference in your ultimate sonic results.

 Let's move on to the power supply capacitors. These capacitors are the filters in the power supply and they play a critical role in the function and reliability of the unit. The original caps were multi-section cans which house several capacitor values in one unit. When I first started doing restorations on these amps several years back, multi-section cans of the correct value were either hard to find or they were new-old-stock, old caps that hadn't yet been installed. Since time is the enemy of capacitors, installed or not, those were not particularly appealing. I decided that it was best to epoxy individual capacitors into the chassis to replace the cans. Presently, a wider range of multi section cans is available, and I don't doubt that some of them are very good but problems remain. When you are dealing with multi-section cans that are visible above the chassis, your new can must look very much like the original, and must mount seamlessly, or you will lose the "original" appearance. I have an MA-230 in my personal collection which has a blue capacitor which doesn't quite fit mounted visibly above the chassis. My attention focuses right on this obvious anomaly whenever I look at the unit and I REALLY don't like it. In such cases, it is better to leave the original can in place for appearance sake and to install replacements under the chassis. Additionally, as is the case with the coupling capacitors, there is a wide range of esoteric and very premium power supply capacitors available. These will almost always require creative mounting.

After all of the capacitors are in place, the job is getting close to being complete. In the units that have a solid rectifier, I like to replace the diodes with new ones. Additionally, these guys all use a selenium rectifier for the negative bias supply. This should be replaced with silicon. Now, about that multitude of resistors wired into the board. McIntosh used high quality carbon resistors when they built these amplifiers. After all of the caps have been replaced, any performance defects are usually traced to a resistor that has opened or changed value. Frequently, all of the resistors are within spec. Some folks take the position that all of these resistors should be replaced with something more modern. I usually do not do that, for two reasons. First, unlike capacitors, resistors are not automatically bad due to the passage of time. I think it is critical to preserve the original McIntosh sound so I am more comfortable leaving the resistor networks in place as experience has shown them to be reliable. Some of you out there may take issue with this, and I will admit that my attitude may be more emotional rather than scientific, but I still have a soft spot in my heart for the old carbons. The second reason is more practical. When I see a unit on which someone has changed all of the resistors, they almost always do it by clipping off the lead to the original part leaving enough space left to tack the new resistor to the old lead. (This is often done with the caps as well). This is all wrong and sinful. The resulting work is a bit haphazard, and is usually ugly as well, very ugly. When replacing any parts on this style of board, it is critical to remove the lead from the old part all the way back to the eyelet of the board and affix the new lead there. While you are at it, it is a good idea to align the parts and bend the leads in such a way that it is pretty when it is complete. After all, these amplifiers are special and valuable so extra time spent to make them look nice is worth the effort. The bottom line here is that to replace all of the resistors and to do a worthy job of it is pretty intricate and quite a bit of extra time and effort is required.

 Performance testing is next, and it is much like what we did at the beginning. Power supply voltages should match what is in the manual. The bias on the outputs should be stable on all four output tubes. Since the unit now has known good caps, this is the time to check the plate current of the outputs and decide whether you like them or not. Whether an output tube is new or vintage, the plate current of the four outputs should not vary a great deal. If one of them is very dissimilar to the others, you must try it in a different socket to confirm that the tube itself is the problem. If it is, then you must consider a different tube or set of tubes. If you purchase new matched pairs, you can expect that they will in fact match each other. I personally prefer vintage tubes when possible, and checking them on a tube tester only goes so far, so the plate current test is very important. Next, is the final performance test. Once again, using the load resistors and the audio generator, the quality of the wave needs to be checked on both channels at both high and low levels. At all times, the wave should be well shaped and pretty with no hum apparent from the power supply. At 400hz, the clipping point should be a good 20% above rated power. A distortion analyzer is the best way to check this out, but if you don't have one, a visually pretty wave usually means you are in spec. These unit do not frequently have subtle performance defects. They are normally either just fine or obviously in trouble.

 The final performance test always is the subjective test. Your ears are very precise test instruments. Plug the unit in and listen critically. The final burn-in is very important and sometimes subtle problems pop up, so paying attention to how it sounds is important. It is also a good idea for a while to glance at the output tubes from time to time to make sure that none are overheating, that is that the bias is stable. I also like to feel the transformers to see how hot they get over time. The output transformers don't warm up all that much, but the power transformer can get pretty hot after a few hours. After doing quite a few of these, you get a sense of just how hot it should be. Once a unit has been burned in for a day or two, if nothing is amiss, you can bet that it will be an excellent performer for the long haul. That is our reason for going to all this trouble. Yes, the time has come to heft the old 240 out of the closet and consider placing it back into service. It will perform as well as any number of expensive things you could buy now......not to mention the poetic justice of having it back up and running. Thanks, Bill