McIntosh C28 - Finding Capacitors close to original specs!

O

OUTCAST

Enthusiast
Hey guys, I am planning to change the capacitors on the power supply side of my C28 preamp that has a buzzing sound coming from it when powered on. I ordered a kit from eBay and after taking an inventory of the caps that were included I've decided I need to shop for some better caps. Does anyone of you have any suggestions?
 
highfigh

highfigh

Audioholic Slumlord
Hey guys, I am planning to change the capacitors on the power supply side of my C28 preamp that has a buzzing sound coming from it when powered on. I ordered a kit from eBay and after taking an inventory of the caps that were included I've decided I need to shop for some better caps. Does anyone of you have any suggestions?
Does it buzz when only the power cord is connected and it's powered on? If so, that's likely the power transformer or maybe (fairly unlikely) some kind of mechanical connection is loose.

If it buzzes when connected to a power amp and speakers, I would ask when the buzz started and if the two are powered by the same outlet.

These are power supply caps- they don't affect the sound unless they're far out of spec but this should be addressed by checking their ESR and connecting the preamp to an oscilloscope, to see where the problem lies.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Hey guys, I am planning to change the capacitors on the power supply side of my C28 preamp that has a buzzing sound coming from it when powered on. I ordered a kit from eBay and after taking an inventory of the caps that were included I've decided I need to shop for some better caps. Does anyone of you have any suggestions?
If you present your question like that, you have no clue how to do this job. You need professional help. You can't even ask the question in a way that can be answered.
 
O

OUTCAST

Enthusiast
Does it buzz when only the power cord is connected and it's powered on? If so, that's likely the power transformer or maybe (fairly unlikely) some kind of mechanical connection is loose.

If it buzzes when connected to a power amp and speakers, I would ask when the buzz started and if the two are powered by the same outlet.

These are power supply caps- they don't affect the sound unless they're far out of spec but this should be addressed by checking their ESR and connecting the preamp to an oscilloscope, to see where the problem lies.
Yes, it buzzes when only the power cord is connected and it's powered on. I'm thinking it's a ground hum issue. So I'm planning to go through all the grounds.
 
O

OUTCAST

Enthusiast
If you present your question like that, you have no clue how to do this job. You need professional help. You can't even ask the question in a way that can be answered.
LOL!!! Settle down there big guy, I didn't mean to rustle you all up. Yes, this is somewhat of a new hobby that I am learning more about. Perhaps I know a little more than I lead on. I was simply looking for a vendor recommendation that maybe someone has worked with in the past and has supplied quality caps.
 
lovinthehd

lovinthehd

Audioholic Jedi
Sounds more like a transformer issue than a ground loop or capacitor issue....
 
TLS Guy

TLS Guy

Seriously, I have no life.
LOL!!! Settle down there big guy, I didn't mean to rustle you all up. Yes, this is somewhat of a new hobby that I am learning more about. Perhaps I know a little more than I lead on. I was simply looking for a vendor recommendation that maybe someone has worked with in the past and has supplied quality caps.
The problem is we can't read you mind. I downloaded the service manual, and it is a complex unit. You will need significant test equipment. A shot gun repair is not recommended. Even replacing the caps in the two power supplies would be a major undertaking. Only the value of the caps is specked. So you would have to read the other specs off the cans. You will need to know heat tolerance leakage, ripple and issues like this.

Vintage restoration almost always turns into a major, time consuming endeavor. I have been through it a number of times. It is not getting easier, as obtaining parts of original specification is an increasingly difficult proposition.
 
O

OUTCAST

Enthusiast
TLS Guy, I agree with you 100%. The shotgun approach is not the answer, and yes, obtaining parts of the original specification is an increasingly tricky proposition. That is why I reached out for vendor recommendations of who might stock the caps I want. Mouser and Digi-Key both have great search tools where I can compare capacitors and view specs like dimensions, ESR, Operating Temps, Ripple Current values, etc... I was running into the problem that they don't seem to have the capacitance, tolerance, and voltage ratings I want. I think the recap is needed regardless because the old capacitors appear to be all original (50+ years old).
The Preamp is in excellent cosmetic condition. The seller told me that her late father purchased it new, and it was one of many McIntosh pieces that he had. Here's a top view and bottom view of the unit. The one thing that stands out to me is that the transformer does not have the McIntosh schematic sticker on the transformer.
 

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highfigh

highfigh

Audioholic Slumlord
Yes, it buzzes when only the power cord is connected and it's powered on. I'm thinking it's a ground hum issue. So I'm planning to go through all the grounds.
TLS Guy, I agree with you 100%. The shotgun approach is not the answer, and yes, obtaining parts of the original specification is an increasingly tricky proposition. That is why I reached out for vendor recommendations of who might stock the caps I want. Mouser and Digi-Key both have great search tools where I can compare capacitors and view specs like dimensions, ESR, Operating Temps, Ripple Current values, etc... I was running into the problem that they don't seem to have the capacitance, tolerance, and voltage ratings I want. I think the recap is needed regardless because the old capacitors appear to be all original (50+ years old).
The Preamp is in excellent cosmetic condition. The seller told me that her late father purchased it new, and it was one of many McIntosh pieces that he had. Here's a top view and bottom view of the unit. The one thing that stands out to me is that the transformer does not have the McIntosh schematic sticker on the transformer.
By "they don't seem to have the capacitance, tolerance, and voltage ratings I want", does this refer to the parts suppliers?

As TLS Guy mentioned, this will require more than just replacing parts- any time components that are important need replacement, the unit's performance must be checked.

BTW- 'old' doesn't necessarily equal 'faulty'. FWIW, when I asked the service manager of an AV dealer who had been trained to service McIntosh equipment since the early-'70s BY McIntosh about his thinking on recapping for the sake of it, he said "If it's not broken, don't mess with it".

Find the source of the buzz- it's more likely to be a transformer or loose nut/screw than from a cap.
 
slipperybidness

slipperybidness

Audioholic Warlord
Hey guys, I am planning to change the capacitors on the power supply side of my C28 preamp that has a buzzing sound coming from it when powered on. I ordered a kit from eBay and after taking an inventory of the caps that were included I've decided I need to shop for some better caps. Does anyone of you have any suggestions?
Mouser is likely the best, and I have a hard time believing they don't have the parts you need.

Digikey is good, but they tend to be a little more $ vs. mouser.

I also like parts-express.com
but, they don't have near the selection as mouser.

What is it about your ebay kit that makes you say you need better caps????
 
TLS Guy

TLS Guy

Seriously, I have no life.
TLS Guy, I agree with you 100%. The shotgun approach is not the answer, and yes, obtaining parts of the original specification is an increasingly tricky proposition. That is why I reached out for vendor recommendations of who might stock the caps I want. Mouser and Digi-Key both have great search tools where I can compare capacitors and view specs like dimensions, ESR, Operating Temps, Ripple Current values, etc... I was running into the problem that they don't seem to have the capacitance, tolerance, and voltage ratings I want. I think the recap is needed regardless because the old capacitors appear to be all original (50+ years old).
The Preamp is in excellent cosmetic condition. The seller told me that her late father purchased it new, and it was one of many McIntosh pieces that he had. Here's a top view and bottom view of the unit. The one thing that stands out to me is that the transformer does not have the McIntosh schematic sticker on the transformer.
TLS Guy, I agree with you 100%. The shotgun approach is not the answer, and yes, obtaining parts of the original specification is an increasingly tricky proposition. That is why I reached out for vendor recommendations of who might stock the caps I want. Mouser and Digi-Key both have great search tools where I can compare capacitors and view specs like dimensions, ESR, Operating Temps, Ripple Current values, etc... I was running into the problem that they don't seem to have the capacitance, tolerance, and voltage ratings I want. I think the recap is needed regardless because the old capacitors appear to be all original (50+ years old).
The Preamp is in excellent cosmetic condition. The seller told me that her late father purchased it new, and it was one of many McIntosh pieces that he had. Here's a top view and bottom view of the unit. The one thing that stands out to me is that the transformer does not have the McIntosh schematic sticker on the transformer.
I see that unit was produced from 1970 to 1978, so would have been designed in the late sixties. So that is early solid state design.

That explains why the voltages are relatively high.

Now I put your pictures together with the circuit, I see that there are more than one cap to the cans.

With the age of that unit it is certainly possible that the power supply can caps are failing. Increasing ripple leakage in old caps certainly can and does, induce hum.

When I have an older amp failing with hum, the power supply caps are the first thing I check. With equipment of that age, then that is more often than not the cause.

Those old "multi caps" I suspect will be hard if not impossible to source.

I have found Mouser and Digi-key of less and less help in sourcing parts for older gear. I have had better luck lately with Newark. In the last years I have had to source parts from France, Germany, UK and Portugal. You will have to do a prolonged internet search.

However I fear if those tall cans have failed, you probably will not find replacements. In which case you will have to design, and build, an external power supply.

Like this.



Lastly I would try and seek out an experienced restorer who has worked on old Mac equipment. They are often very generous with their advice.

I have never been a Mac fan. In the vintage amp department I have been largely Quad. I think these days, most restorers limit their range of gear. I bet there is someone out there who is expert on your unit. It may well be more profitable to seek out an expert first, who can give you vital tips and guidance.
 
Eppie

Eppie

Audioholic Samurai
I would not expect to find replacements for those tall cans. The restorers I know replace them with appropriate individual caps (if they are multi-caps). For future serviceability, it is better not to empty the cans and try and stuff new caps in them. You can replace the cans, or if you want to preserve the inside appearance, you can disconnect them and install the new caps underneath. Depends upon whether you're set on a historically accurate restoration or just want to get the amp up and running properly.
 
TLS Guy

TLS Guy

Seriously, I have no life.
I would not expect to find replacements for those tall cans. The restorers I know replace them with appropriate individual caps (if they are multi-caps). For future serviceability, it is better not to empty the cans and try and stuff new caps in them. You can replace the cans, or if you want to preserve the inside appearance, you can disconnect them and install the new caps underneath. Depends upon whether you're set on a historically accurate restoration or just want to get the amp up and running properly.
The power supply appears to be duplicated for left and right channels, but with one power transformer. The major power supply caps are triples. Those are C 301 and C 302. The values of the early and late serial numbers are the same. I doubt there is room in there to mount twelve individual caps.
So he really needs to get the advice if a restorer who has done this before.

Early transistor gear is a nightmare now. If it was tube this would be much easier.

The only person who really nailed early transistor amps from the start was Peter Walker in 1969, with his first transistor amp, the Quad 33/303 combo. Those were right from the start, and very reliable. Most I suspect still in use today. I doubt the early McIntosh amps like this, could match that combo. That 33/303 combo is widely recognized as the first design to seriously challenge tube amps.
 
Verdinut

Verdinut

Audioholic Ninja
The McIntosh solid state power amps having a transformer in the output stage cannot match any decent solid state amplifier without one.

I remember that, in the early 1970's, a McIntosh solid state amp, I don't remember the model, could not properly handle Tannoy Dual concentric speakers, with resulting mushy and under damped bass. But when the Tannoys were driven with a Sony TA-3120, an amplifier with a rated power of only 50 watt/Ch at 8 ohms, they were brought to life and they could reproduce tight bass as originally recorded.
 
Eppie

Eppie

Audioholic Samurai
The power supply appears to be duplicated for left and right channels, but with one power transformer. The major power supply caps are triples. Those are C 301 and C 302. The values of the early and late serial numbers are the same. I doubt there is room in there to mount twelve individual caps.
So he really needs to get the advice if a restorer who has done this before.

Early transistor gear is a nightmare now. If it was tube this would be much easier.

The only person who really nailed early transistor amps from the start was Peter Walker in 1969, with his first transistor amp, the Quad 33/303 combo. Those were right from the start, and very reliable. Most I suspect still in use today. I doubt the early McIntosh amps like this, could match that combo. That 33/303 combo is widely recognized as the first design to seriously challenge tube amps.
I didn't have time to find the schematics, but yes, replacing cans in old tube gear is much easier as there is usually a fair bit of room in the underside of the chassis. Much tighter quarters in solid state gear.
 
highfigh

highfigh

Audioholic Slumlord
Which caps are in each can? Antique Electronic Supply has the old machines used by Mallory to make multi-segment caps- they have a wide assortment of values and even for higher voltages, since the majority of their customers are replacing capacitors in radios and amplifiers that have tubes. I have bought caps from them several times- they have tested well and have been in use for more than ten years without problems.

Here's their website-

https://www.tubesandmore.com/
 
O

OUTCAST

Enthusiast
Thanks, guys. I do appreciate everyone's opinions and I will definitely seek out the advice of a competent restorer with proper test equipment. I'll take my time with this restoration, and yes, I do want to keep it as original as possible. For now, I'm happing with my Yamaha preamp so I will not rush the restoration. I will try to update this thread whenever I've made some progress sorting the unit out.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Thanks, guys. I do appreciate everyone's opinions and I will definitely seek out the advice of a competent restorer with proper test equipment. I'll take my time with this restoration, and yes, I do want to keep it as original as possible. For now, I'm happing with my Yamaha preamp so I will not rush the restoration. I will try to update this thread whenever I've made some progress sorting the unit out.
That sounds like a sensible plan.
 
highfigh

highfigh

Audioholic Slumlord
I was talking about recapping equipment with a service tech yesterday (yeah, they actually exist) and he mentioned companies like Panasonic using non-standard capacitance values in their equipment, then trying to find replacements years later. So many people seem to think these are precision components, but if someone were to read the specs, they would find that the value is often stated with +20%/-70% tolerance. Resistors can be anywhere from a tight tolerance to more than 10% deviation.

Bottom line, don't sweat the value so much, especially in power supply filter caps. Don't pick something that's so far above the OEM capacitance that it causes problems on power up, but ±10% will never hurt anything. If you overshoot on anything, do that with the working voltage rating. If anyone wants to claim "But, but, but...IT'S NOT LIKE THE ORIGINAL PARTS!!!!!!!!!!!!!", tell them to hit the road.
 

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