I'm upgrading a Forte power amp and recently bought some large surplus electrolytic caps. These replacements are 47,000uf, where the originals were 15-18,000uf.
I understand the date code indicates they were made around 7 years ago (these were purchased "new" in the box from surplus).
I've read where it was recommended "ANY electrolytic more than about 12-15years old should be replaced."
As these were stored for approx 7 years, does it mean they won't last more than 5-8 years once in use (or should I expect 12-15 years of actual use)?
Also, since these have never been used, I've been advised to "form" them using a series resistor(20-30kohm) and variac to gently bring up the DC voltage to the needed level(then discharge them gently through the resistor).
Any advice/experiences regarding this are appreciated.
-Chas
I understand the date code indicates they were made around 7 years ago (these were purchased "new" in the box from surplus).
I've read where it was recommended "ANY electrolytic more than about 12-15years old should be replaced."
As these were stored for approx 7 years, does it mean they won't last more than 5-8 years once in use (or should I expect 12-15 years of actual use)?
Also, since these have never been used, I've been advised to "form" them using a series resistor(20-30kohm) and variac to gently bring up the DC voltage to the needed level(then discharge them gently through the resistor).
Any advice/experiences regarding this are appreciated.
-Chas
I would not hesitate in trying out these capacitors they should be fine, especially if you 'reform' them. Most quality electrolylic resevior capacitors should survive up to 20 years on the shelf - Capacitor life is severely shortened when they reach high temperature in use.
Are you sure that the rest of the amplifier is up to the increase in inrush current at switch on
Are you sure that the rest of the amplifier is up to the increase in inrush current at switch on
Caps mostly get old in use and/or with elevated temperatures. Sitting around they age and very slowly deteriorate. 25 years and most still seem to work. Thing is these new low ESR high speed caps are so much better than anything from even 5 years ago in these big value available now. Just switched to 100,000µF switching caps for rebuilds. Yes they are better in about every way and yes they test and sound better also.
Well, the power transformer is HUGE, and the 2 bridge rectifiers look like at least 20A units (photo of similar amp is attached). It appears that there is a current-limiter (thermistor?) before the power transformer, so I hope its safe to triple the PS caps.
I'm thinking about replacing the bridges with some of the way-cool HexFRED units- should I go for the 27A or the 32A rated units?
Any experienced advice here is appreciated.
-Chas
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a lot have to do regarding endurance the way and the quality of built
in the times of vintage service were most of electrolytics of most of our costumers getting replaced anyway then the "broken" parts some times we test with various methods and surprize surprize still work like hell
some companies did an excellent job regarding power supply capswhile some others did horible choices for their machines
i have sen models of nakamichi working for 25 yeras and almnost all caps are with in tollerance and seen models of the same company that worked for 15 years and all caps inside was cr**p
repeatative presence of the specific equipment with the same problem again and again shows that the caps was the wrong choise in the first place ... presumably the company didnt know about it
in the times of vintage service were most of electrolytics of most of our costumers getting replaced anyway then the "broken" parts some times we test with various methods and surprize surprize still work like hell
some companies did an excellent job regarding power supply capswhile some others did horible choices for their machines
i have sen models of nakamichi working for 25 yeras and almnost all caps are with in tollerance and seen models of the same company that worked for 15 years and all caps inside was cr**p
repeatative presence of the specific equipment with the same problem again and again shows that the caps was the wrong choise in the first place ... presumably the company didnt know about it
I have literally thousands of capacitors, mostly surplus, from nearly new to as old as dirt. The only ones that show any signs of deterioration are the HV twist locs up at 450 volts or so. Anything else can be pulled from its box, bin or bag and used without forming or anything else. The HV caps need to be slowly formed if any reliability is to be had. Newer brand name caps are better, not because they're newer, but because they're just made better from day one. Technology has advanced. Newer off-brands should be approached with caution. As I've said many times before, the best practice is to build (or buy) a simple bridge and measure the things. If C and D are good, and leakage is low at full voltage, you've got nothing to worry about.
Conrad
Conrad
I started my electronics career in 1974 and have yet to replace a bad "computer grade" capacitor. I have milk crates full of them that I pick up when I find a good deal at surplus stores. If there is no physical damage I don't think twice about buying them. They are usually only a couple of bucks apiece so you can get a couple of amps worth for the price of a new one. Just reform them before you use them if are worried.
Craig
Craig
Electrolytic caps
I've replaced a lot of 440 VAC motor drives under 5 years old where the electrolytic caps leaked out into the bottom of the box, then the drive quit working on cold mornings. Quality brand motor drives usually last more like 10 years before the caps explode. Half the electronic equipment I replaced in the factory had visible electrolytic cap problems. I just replaced every electrolytic cap in my new 1968 Hammond organ, it has quadrupled the volume, lowered hum by half, increased the high frequencies, and restored function to the percussion circuit that was inaudible when bought. Hammonds and Leslies made in the 50's are known to explode the bottom out of can caps. Spend your money where you want, I'm buying new caps from a distributor that puts a discount symbol next to the line if they are over 18 months old. Notice new caps come in various lives, 500 hours to 10000 hours. I pay extra for the ones labled to last thousands of hours. When I do so, I receive the brands and appearance that mostly I saw in the long life motor drives.
I've replaced a lot of 440 VAC motor drives under 5 years old where the electrolytic caps leaked out into the bottom of the box, then the drive quit working on cold mornings. Quality brand motor drives usually last more like 10 years before the caps explode. Half the electronic equipment I replaced in the factory had visible electrolytic cap problems. I just replaced every electrolytic cap in my new 1968 Hammond organ, it has quadrupled the volume, lowered hum by half, increased the high frequencies, and restored function to the percussion circuit that was inaudible when bought. Hammonds and Leslies made in the 50's are known to explode the bottom out of can caps. Spend your money where you want, I'm buying new caps from a distributor that puts a discount symbol next to the line if they are over 18 months old. Notice new caps come in various lives, 500 hours to 10000 hours. I pay extra for the ones labled to last thousands of hours. When I do so, I receive the brands and appearance that mostly I saw in the long life motor drives.
You got it right. This thread is quite timely to me. I was toying with the idea of starting just such a thread. There is no shortage of people that are sure electrolytic caps go bad. I tend to disagree, and it was nice to find that paper seems to confirm what I believe. It is also nice to hear from others that feel the way I do.
In the amplifiers serviced here we are certain many of the electrolytic caps go bad from testing those very caps. Actually, ripple current seems to kill most of them. 10 years of service when the amp is used almost daily we find dead electrolytic caps.
I only serviced equipment for friends the last several years I could work, but some of that was over 40 years old. I have only found one bad electrolytic cap. I'm sure I haven't seen as many pieces of service gear as you, but I do have a capacitor analyzer that checks for value, leakage and ESR. I don't doubt that you have seen many bad caps. It sounds like you service electronics, so you see a disproportionately large sample of equipment that has failed to operate properly. As sakis pointed out, some brands or models have more problems than others. I suspect that is primarily because the manufacturer cut cost by selecting electrolytic caps that weren't of sufficiently high quality. I believe you are correct about ripple current and the resulting temperature rise being the cause for failures. I also believe that proper selection of capacitors will prevent this.
I tend to agree with you Steve and sumaudioguy. Actually, caps in audio have an easy life when compared to those used in photoflash.
It's not uncommon to blow caps in some of these high powered flash generators, especially those fast charge "transformerless" types. Caps are charged to 800V to 1,000V directly from the Mains and dumped instantaneously when the camera is fired. When a 3,000 joules pack blows, its pretty dramatic.
ha ha ha ha ...Steve ...i dont know what you are doing these days but if you pop up in my company you will need to second think this .....
please notice we never service equipment older than 30 years ...actually we hardly ever repair machines that are capacitor coupled in the output ...
Trust me any brand marantz pioneer nakamichi akai teac and many many other go for a total recaping ...at least all the small ones at this age
we normally service 150 amps a year .... trust me when i go to the parts shop the people look at me with a big smile !!!!
rebuilt 1200b scope today
Just rebuilt an HP 1200b scope today and 2 of the main supply caps still tested good. One was far out of spec.
In a rebuild all electrolytic caps are replaced here. Sort of a shotgun approach as we are sure we got the bad ones. The result is good reliability. We like the high temperature 105°C or higher and high ripple switching type.
Before someone says something about rebuilding such an old scope and why bother, the answer is two channels of differential inputs with 100µV/div sensitivity. 500kHz bandwidth is great for power supply and low noise work.
Just rebuilt an HP 1200b scope today and 2 of the main supply caps still tested good. One was far out of spec.
In a rebuild all electrolytic caps are replaced here. Sort of a shotgun approach as we are sure we got the bad ones. The result is good reliability. We like the high temperature 105°C or higher and high ripple switching type.
Before someone says something about rebuilding such an old scope and why bother, the answer is two channels of differential inputs with 100µV/div sensitivity. 500kHz bandwidth is great for power supply and low noise work.
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I used to work in service, though not audio. Eventually it drove me crazy (it doesn't show does it?) because I became convinced that everything was junk. Obviously the only things that come through service are the things that don't work. You have to be careful trying to get a good statistical picture from a subset called "broken". OTOH, of things that fail, caps are way high on the list, as are mechanical connections of all sorts. IMO, you have to be careful specifying caps, as ripple current can raise the internal temperature and shorten life dramatically. That 85C number is way easier to reach than most people think, though audio equipment should never stress caps if the designer had a clue. Sadly, I don't think they physically measure ripple current even in most commercial equipment, and that's the only way to be sure of what's happening. Most caps get picked by rule of thumb and sometimes that rule is wrong. I've worked for electronic companies for 35 years and have never seen anybody (except me) measure ripple current in a power supply cap. Go with brand names and measurements. If the cap is properly applied, made well and tests good for all its parameters, it will last for decades.
Conrad
Conrad
Here here. When designing I measure current of every lead of every device including grounds!
The only way to know for sure, period.- Status
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