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Old 7th January 2015, 08:37 PM   #1
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Default Mcintosh C2200 ReCap

I am replacing all electrolytic caps in a C2200 and there are over 50 electrolytics in the signal path alone. Are the "Audio Grade" caps worth putting in? I was looking at the Elna SILIMIC II to replace the general purpose Rubycon YK series that are in there now.

The amplifier isn't mine. It belongs to a good friend of mine, he tells me that once in a while the right channel gets quiet and distorted. I have had the amp at my house hooked up to an oscillator and a loaded the output with 100k load (his power amps input Z) and I can't get it to misbehave. I have tried for 40 hours. Anyway he has had the amp for 10 years and might sell it soon so he wants to clean, retube, recap, and rebulb the amp.
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Old 7th January 2015, 10:20 PM   #2
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Probably the cabling or amplifier is at fault. Why do you want to tinker with a good design?
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Old 7th January 2015, 10:48 PM   #3
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I don't think it is the cable or the amplifier. My buddy said when it happens the meter needle drops for that channel (right) no matter what input source was selected. Just to be sure he tried reversing the left and right inputs, still same channel was dead. He also said he tried reversing output interconnects going to the amp left and right, sound would come from the right channel now and not left, so it is the preamp right channel for sure.

He doesn't really want to tinker with the design, just replace the caps with a finite life span that degrade over time. I saw several 85 degree 100uF lytics' up pretty close to the tube sockets. Figure if the problem is so intermittent just replace all things that age poorly, listen to it for a while and see if it cures it. Of course if the problem would just present itself for me to look at it I could track it down a lot easier. Pretty much just guessing at this one but also do a little "maintenance" at the same time.
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Old 8th January 2015, 12:00 AM   #4
Keit is online now Keit  Australia
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In proposing to just replace every cap, you are going about it the wrong way. You should FIRST identify excatly what the fault is, which part it is - no matter how hard that may be. It is all too easy to add additional faults by error if you just go replacing willy nilly. Many a good piece of electronics has been abandoned because of this, or given to a professional to fix at enormous cost.

In fact experience has long taught me that if someone comes to me with an amp, radio, or whatever that he has replaced every capacitor willy nilly, and it has a fault it didn't before, I usually refuse to help - it just chews up too much time.

With intermittent faults that the owner reports that you have yet to see, there are two main ways to sort it out:-
a) while playing a tone from an oscillator through the system, gently, with an insulating stick, move parts about and tap them. This will reveal PCB cracks, dry joints, and other mechanical faults.
b) Selectively squirt small amounts of freezer on parts untill you find the temperature sensitive one that brings on the fault. You can buy small pressure pack cans from electronic parts stores for just this purpose. This method works reallly well with solid state equipment but its good with tube equaipment as well. DO NOT allow freezer to get on tubes, and don't squirt transformers - it's pretty much a waste of time.

When the owner reports an intermittent fault that won't re-appear, its usually a mechanical fault. Vibration in transporting it tio you may temporarily make it come good.

Don't overlook that the fault may not be in the amp - it may be in cables or other gear that the owner used with it but didn't give you.

Faults such as you describe are often tubes, or grid coupling capacitors if the amp is very old. Professional techs build up experience that tells themn certain brands of cap never fail, and ceratin caps in certain amps nearly always fail.

I NEVER replace electros willy nilly in equipment made in the 1960's or later. Electros made in the 1960's and later, when made by reputable manuafctuers such as Philips, most USA makers, and the Japanese manufacturer Elna are very reliable. British brands such as Ducon are crap.

Last edited by Keit; 8th January 2015 at 12:05 AM.
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Old 8th January 2015, 11:13 AM   #5
DF96 is offline DF96  England
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Hot electrolytics don't usually go intermittent, they go low in value and high in ESR.

Read post 4 very carefully. Follow its advice.
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Old 8th January 2015, 11:29 AM   #6
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I have been repairing electronic equipment for 50years and have never heard of the brand name Ducon. Sorry.
Sprague, Mullard, ITT, Daly etc. were always good makes. Ducilier were French.
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Old 8th January 2015, 12:06 PM   #7
Keit is online now Keit  Australia
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John, given that you are located in England, if you haven't heard of Ducon (in its later years a division of Plessey), you must have had a very sheltered life! They were very common in consumer equipment in the 1950's, 60's and early 70's. Perhaps you repaired professional grade equaipment.

Mullard is what Philips was known as in England, for historical reasons and out of respect for Stanley Mullard, who was on the Board for about 60 years. When Stan Mullard finally died, the Mullard name was dropped.

Dubilier was another barnd made in both USA and UK. The UK made Dubiliers for consumer equipment were even more crap than Ducon, but they also made capacitors to higher standards for professional equipment. Another British capacitor brand was Erie (ok but not as good as Mullard/Philips)
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Old 8th January 2015, 05:59 PM   #8
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Well I didn't think it was a bad idea to replace the electrolytic caps (unless I was really bad at working with PCB's) but oh well, I will hold off until I find the fault. A mutual friend loaned him a Soundcraftsman preamp so I can look at the Mcintosh longer.

I was told that the freeze spray was bad for components and to not use it by an old TV repair man I will pick up a can and give it a try, obviously I won't be spraying the tubes

So I guess I was wrong about electrolytic capacitors, they can have a life span of 50 years without degrading, who knew
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Old 8th January 2015, 10:20 PM   #9
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Made a chilly run to RatShack and picked up some freeze spray. I had a good laugh at the register.......buying freeze spray on the coldest day in the last 6 years lol, as if it's not cold enough.

Anyway, I got to thinking, he has his preamp on the shelf directly above his tube power amp and heat rises. So now I placed a heating pad under the preamp hoping to heat up the faulty component. If I see a fault I will systematically freeze a component to see if the fault goes away.

Before posting I had already poked around looking for a bad connection/solder joint during the 40 hrs of bench testing. I will still do this under the now warmer environment.

If he sells it he isn't going to do the caps, just the repair. If he keeps it he might upgrade them down the road.
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Old 8th January 2015, 11:24 PM   #10
rayma is offline rayma  United States
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Quote:
Originally Posted by famousmockingbird View Post
Before posting I had already poked around looking for a bad connection/solder joint during the 40 hrs of bench testing. I will still do this under the now warmer environment.
BTW, the troubleshooting described does not rule out bad cables between the preamp and power amplifier. You have to swap L and R cable ends first
at the back of the preamp for the first test, and then for the next test at the power amp inputs, to be sure. Or, just replace them with different cables
if problem is very intermittent.

Last edited by rayma; 8th January 2015 at 11:33 PM.
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