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Capacitor lifespan
- Thread starter agedhorse
- Start date
@agedhorse
Thanks for starting this thread and providing the information. May I ask, whether the capacitor in the pictures below, with which I replaced the stock cap in my 2008 Fender AmStd Pbass, is an electrolytic capacitor? I only remember it is a Philips and of higher value than the stock one. I do hope it's not an inappropriate capacitor for a bass guitar...
Thanks for starting this thread and providing the information. May I ask, whether the capacitor in the pictures below, with which I replaced the stock cap in my 2008 Fender AmStd Pbass, is an electrolytic capacitor? I only remember it is a Philips and of higher value than the stock one. I do hope it's not an inappropriate capacitor for a bass guitar...
- Feb 12, 2006
- 61,035
- 5
- 220,950
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
it’s running our shop speakers, it’s a fairly light load. The amp is a Genz Benz ML-200.
I just realized that the clock-radio has been running 24/7 for ~35 years and the electrolytic caps are still functioning fine. That’s ~1/2-million hours. The thermostat in the shop, which also has electrolytic caps has been working 24/7 for 17 years, again no issues.
My point is that the folks insisting that caps only last 10-15 years (in intermittent duty no less) are in general full of crap. There are entire industries where there are examples contrary to this premise. For example, airport and hospital PA systems operate 24/7 for decades without replacement of equipment.
That’s a film cap, in that application it should last 100+ years.
Imo it's sort of idiotic to put a lifespan on such things anyways. From my very limited ignorant experience, most electronics either fail after a very short time, or go on for literal decades. It probably depends a lot on what is being used, but I've seen plenty of computers that have been used daily for over 30 years, that still run just fine. On the other hand, I've heard that plenty of rockstars need constant maintenance on their amps, but they're obviously running them exceptionally hot in those cases.
For your entertainment pleasure, a madman converts a bell alarm clock to an electrolytic capacitor alarm clock:
Some people inherently have a problem with true and tried science!
I bought a Trace Elliot V4 a few years ago that was “New Old Stock” and a few people told be to have the capacitors replaced because they had just been sitting unused. When the amp came in I used it for a bit and the fuse popped! I took it to my tube guy and he told me that the only issue with the amp was that it was over biased. He biased it and it’s been great since!
Andy, what do you recommend for older tube amps that have not been used in years? Do these amps need to be brought up to line voltage slowly with a Variac? What about just running the line voltage down by using some incandescent bulbs so the that start up is say 110 - 110 VAC?
I've got a 53' Champ amp that I'd like to use again. It was working properly when I put it in a display case about 20 years ago and don't want to be the cause of a problem. TIA
Mainly talking about vintage stuff that has sat for years without use. Whether that is true for more modern caps, I don't know. I base this on comments from people with more knowledge than me talking about electrolytics needing to be reformed or replaced in old equipment if they have not been used in many years. I can't point to any specific example without spending time trying relocate that info. I don't know if this would apply to more recent stuff say in the past 20 yrs or so that has sat unused for that long. In my opinion, it's cheap insurance to replace the caps in older, unused gear to avoid a potentially expensive repair.
You’re more forgiving than I was. The main reason I asked what a client had already done when they first attempted to “fix” the problem was to get an idea of what else (in addition to the original problem) had now also been broken.
From my experience, very few things ever damage something as badly as a botched repair attempt. Instead of labeling panel latches with the word OPEN it’d be better if they used the word THINK.
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Stuff that has been unused for many years can be an issue, as the capacitors are unbiased for long periods of time. I have a couple mixers that I use for live work (I have two so I have a backup). Rather than have one sit on a shelf (which means the backup probably wouldn't live as long as the other one, thus defeating the reason for a backup at some point), I rotate them every year - they have tags on them that designate one as the "odd year" unit, and the other one is used on even years.
So... guess I'll go fire up that old tube amp in the basement and see what happens
Thanks @agedhorse for the discussion, as MTBF and factors affecting parts lifespan is generally lost on anybody who isn't a specialist or an engineer.
Thanks @agedhorse for the discussion, as MTBF and factors affecting parts lifespan is generally lost on anybody who isn't a specialist or an engineer.
Jazzdogg
Less barking, more wagging!
At one point I used to repair arcade machines. The switching power supplies that they used at the time did frequently have issues with caps going bad. The main cause seemed to be that they were bunched together next to some heatsinks that put off allot of heat. They would fail with high ESR. Replacing them would get the supply back up and running.
We also used to be able to buy "cap kits" for several of the popular CRT monitors that were used at the time. These also seemed to fix various issues. But again, it was high ESR failure of devices placed near heat sources.
Probably all due to under-spec'd caps or poor design choice.
I say all this because I have a feeling that there are instances like this in other areas that cause techs to make broad generalizations that "caps have a high failure rate". These are probably the same techs that complain about engineers all the time.
Lots of folks seem to confuse correlation with causation.
Certainly Mesa Boogie amps - I've seen a Mark IIA, that still has the original caps -- would that be 1974 or earlier. And they look like they go on forever. I've seen pre CBS blackfaces twenty years or more ago that have the bulging caps. They also had extraneous noise. But what do you expect if you used carboard. But as you know people wax poetic on those oil and paper caps.
Currently I have the Mark IV , Studio 22 (my oldest - the manual was laid out on a typewriter) Bass 400 and Blue Angel. I will probably die before they need cap jobs. Studio 22 was a house amp in one of the old country music dance halls here, so was used hard. It only needed the tube sockets cleaned and 2 input jacks replaced. It looks beat but sounds good.
Currently I have the Mark IV , Studio 22 (my oldest - the manual was laid out on a typewriter) Bass 400 and Blue Angel. I will probably die before they need cap jobs. Studio 22 was a house amp in one of the old country music dance halls here, so was used hard. It only needed the tube sockets cleaned and 2 input jacks replaced. It looks beat but sounds good.
Al Kraft
Supporting Member
- May 2, 2016
- 10,771
- 40,450
- Disclosures
- Mesa Boogie beta product tester and player support
And this is the other side of the coin where an engineer makes a bad parts choice to top off a poor design approach and the techs are ones who have to face the customers. I absolutely agree that there are certain products with known design weaknesses that make it into the hands of customers.I say all this because I have a feeling that there are instances like this in other areas that cause techs to make broad generalizations that "caps have a high failure rate". These are probably the same techs that complain about engineers all the time.
In early GM high energy ignition system designs the original rotor design was made of a material that was subject to early failure by dielectric puncture. In some cases it would even fry the electronic module in the distributor. It didn't take a lot of troubleshooting and was a first place to look when a customer complained of a badly running vehicle or the vehicle wouldn't start.
The engineers finally came up with replacement parts that were up to the task, but not before plenty of techs got an earful they didn't deserve from rightfully angry customers.
Modern capacitors are way better than some of the old ones. I have equipment that dates back 90 years with the original caps still working.
All capacitors are not created equal. Some are good, some are not. Some are junk or even knockoffs that don’t meet their data sheet specs. So you have to be careful. Not all products are well designed. If the design has issues or the electrolytic capacitors are note well chosen, there can be problems. Dell computer spent many millions on recalls related to bad capacitors. Things happen.
How a stolen capacitor formula ended up costing Dell $300m
A lot goes into a capacitor design and specification. See in the second document, Section 2-2, Failure Modes.
Even though a cap has not failed, it can degrade over time. It’s important to inspect equipment to ensure that components are performing up to spec rather than wait for a catastrophic failure to occur.
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec2.pdf
All capacitors are not created equal. Some are good, some are not. Some are junk or even knockoffs that don’t meet their data sheet specs. So you have to be careful. Not all products are well designed. If the design has issues or the electrolytic capacitors are note well chosen, there can be problems. Dell computer spent many millions on recalls related to bad capacitors. Things happen.
How a stolen capacitor formula ended up costing Dell $300m
A lot goes into a capacitor design and specification. See in the second document, Section 2-2, Failure Modes.
Even though a cap has not failed, it can degrade over time. It’s important to inspect equipment to ensure that components are performing up to spec rather than wait for a catastrophic failure to occur.
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec1.pdf
https://www.nmr.mgh.harvard.edu/~reese/electrolytics/tec2.pdf
I was divesting myself of an old 80s BGW amp (clean and working!), and some bozo wanted to argue with me about capacitors.
Somehow even in the information age people get fixated on lore.
Somehow even in the information age people get fixated on lore.
In some cases data analyzed from accelerated and destructive testing allows calculation of MTBF. Failure rates are plotted. Probabilities are examined using the data and formulas. MTBF is based on a certain acceptable percentage, let’s say 90% as an example, of the products lasting that long.
Having worked with engineers though, I know that many of the so-called "poor design choices" came down to the one thing that is responsible for most bad ideas. Money. Most engineers, given the opportunity would design you a product that would never fail in a million years. The issue is that it would cost far too much. So things are redesigned with cheaper components with cost-savings in mind.
So blaming the engineers that designed it often isn't fair either.
- Feb 12, 2006
- 61,035
- 5
- 220,950
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
In general, "reforming" applies to some early cap designs and also some specialty caps used in motor drives (that operate with high ripple currents) but in general I haven't seen the need nor have I seen any failures related to not doing it. But opinions being rear end orifices, everybody has one on this subject. The less educated and experienced, seemingly the more bizarre the opinion.
Beware that most of those opinions are from folks with virtually no education or real knowledge.
In my experience, far more damage is caused by the act of replacing the caps rather than leaving a perfectly good working amp alone. I see it fairly regularly.
You’re more forgiving than I was. The main reason I asked what a client had already done when they first attempted to “fix” the problem was to get an idea of what else (in addition to the original problem) had now also been broken.
From my experience, very few things ever damage something as badly as a botched repair attempt. Instead of labeling panel latches with the word OPEN it’d be better if they used the word THINK.
I couldn't agree more.
To get an accurate number takes a LOT of work because the models are quite complicated. It looks at variables like temperature, thermal cycling (how wide and how often), expected power quality, the components themselves, how and where the components are used within the circuit, the voltage, current and thermal margins between the component rating and actual conditions, the number of components and how critical they are in the operation (ie. tolerances) etc. This is done for each component, and then they are all factored together.
For a simple example, you have a circuit with 2 components, each necessary for proper functioning and each have a MTBF or 1 million hours. When you combine the 2 components, the expected or unweighted MTBF would be around 500k hours since either of the two components mean failure rate must be factored in and there are 2 chances per 1 million hours or 1 in 500k hours. This all gets into heavy duty statistics and in reality the formulas are simplified to become less accurate but more practical to calculate, and there can be quite a difference with multiple models that are each valid in their own way. Some engineers calculate multiple ways then look for potential weaknesses that drag the number down and address it in the design. The more parts in a design, the more opportunities any single component can fail.
Or accept that most of the folks preaching about capacitor degradation have little working knowledge but spend a lot of time on hobby-internet sites reading about things that have nothing to do with reality (or science).
