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.
