been repairing one Akai amplifier and even though the amplifier is very old filter capacitors never been replaced in the past still to my surprise both capacitance and esr readings was within 15% of the values specified from manufacturer ...
That is quiet amazing for capacitors of almost 30 years and its a phenomenon very odd and rare...In my shop we repair 300-400 amplifiers per year and i think that this must be the first time seen that .
To complete the picture there is also something else very odd about this amp that got me thinking : when you turn off the amp for reasons that i didn't search farther the filter capacitors will remain charged
Obviously secondary circuits consume nothing to very little resulting that the voltage will remain there even after 4 days after that you turned off the amp ( !!!!!! )
Does this situation has something to do with the extended life of capacitors ????? IE if capacitors are charged to rated voltage will live longer that if left with no charge ?
opinions please
Kind regards
sakis
That is quiet amazing for capacitors of almost 30 years and its a phenomenon very odd and rare...In my shop we repair 300-400 amplifiers per year and i think that this must be the first time seen that .
To complete the picture there is also something else very odd about this amp that got me thinking : when you turn off the amp for reasons that i didn't search farther the filter capacitors will remain charged
Obviously secondary circuits consume nothing to very little resulting that the voltage will remain there even after 4 days after that you turned off the amp ( !!!!!! )
Does this situation has something to do with the extended life of capacitors ????? IE if capacitors are charged to rated voltage will live longer that if left with no charge ?
opinions please
Kind regards
sakis
Well, they would not be subject to the large inrush current every time that it is turned on. It reminds me of when I worked for a CRT video projector manufacturer in the early 90's.They were having a hard time to keep them from failing before the end of the warranty period which was six months. One day a customer called to get their projector fixed for the first time and it was 4 years old! We had never had one that had lasted that long before breaking. When we asked them how they were using the projector they said “We never turn it off”.
The voltage across the cap is what builds up and maintains the dielectric.
A discharged or partially charged capacitor breaks down the dielectric to a level that just maintains the leakage current.
Stored capacitors need to reform that dielectric on first recharge.
It seems from this that a reasonable conclusion to draw is that a fully charged capacitor that only loses 10% of it's charge, by the next charge up, will need less reforming. It further seems that the metal that that forms the dielectric will be from very local to the areas most needing reforming. This might lead to fewer very thin patches of metal and even to fewer perforated patches that are likely to occur when severe reforming is performed at every power up.
Thin metal patches and perforated metal seems like a measure of lifetime.
Obviously, I have no data to substantiate any of this.
A discharged or partially charged capacitor breaks down the dielectric to a level that just maintains the leakage current.
Stored capacitors need to reform that dielectric on first recharge.
It seems from this that a reasonable conclusion to draw is that a fully charged capacitor that only loses 10% of it's charge, by the next charge up, will need less reforming. It further seems that the metal that that forms the dielectric will be from very local to the areas most needing reforming. This might lead to fewer very thin patches of metal and even to fewer perforated patches that are likely to occur when severe reforming is performed at every power up.
Thin metal patches and perforated metal seems like a measure of lifetime.
Obviously, I have no data to substantiate any of this.
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I have found that good quality, large size capacitors last forever, provided they are unstressed: either shelf life or gentle conditions usage, ie low temperature, low ripple current, normal operating voltage.
See here for example:
http://www.diyaudio.com/forums/parts/199046-oldies-but-goodies.html
See here for example:
http://www.diyaudio.com/forums/parts/199046-oldies-but-goodies.html
I've worked on a pretty good number of Dynaco Stereo 120 power amps. My experience is that the big power supply and speaker caps in that amp seem to last forever. The smaller signal electrolytics on the amplifier boards are the things that tend to open up (at least in that amp). Perhaps it's because they sit closer to stuff that generates heat.
Still, after 40 years, you wonder...how long can these caps last?
Update My Dynaco
Still, after 40 years, you wonder...how long can these caps last?
Update My Dynaco
It also depends on the purity and stability of all of the capacitor materials and components, especially the electrolyte. The seal technology used matters.
http://www.cde.com/tech/reliability.pdf
http://www.cde.com/tech/reliability.pdf
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