Landfill full of capacitors

RobHolt

RobHolt

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It is common practice today among the audio diy community and certain manufacturers to replace electrolytic capacitors roughly every 10 years - sometimes sooner.

Now up until recently I'd have routinely done the same but had some creeping doubts about this universal servicing requirement. I asked RD for his views on this recently so I think there are at least two of us who question the practice.

ISTM that we should be looking at the stresses placed on the capacitor that reduce useful life, and that these by no means carry equal weight in different circuits and operating conditions.

The main enemies to cap life would appear to be:

- Supply ripple across the device. Capacitors have a maximum ripple rating.

- Exceeding the operating voltage. A maximum is stated on every cap.

- Heat. The hotter the environment the shorter the life, dramatically so at high temperatures and all electrolytic caps carry a max temperature rating.

All three will seriously reduce capacitor working life if exceeded, and all three will still change the life of the capacitor to some degree even if well below those maximum safe limits.

Consider these two examples:

I have a 40wpc Class A valve amp running a pair of KT88s per side and using a valve rectified PSU, capacitor and choke smoothed.
The high voltage capacitor in this valve amplifier is run at around 20% below the maximum voltage rating, very close to the ripple rating and in a case where temperatures exceed 70 deg C.

Not surprisingly, after about two years of regular use this amplifier starts to display some low level electrical hum but just as importantly, the large choke following the first stage capacitor starts to buzz very audibly. Clearly the capacitor is now failing and excessive ripple is entering the choke, causing it to vibrate.
So in this instance we have a useful life of 2-3 years tops.

Now consider something like a Naim Hicap.
It uses two 15,000uf 63v capacitors and ripple across those is well under the max spec. Voltage across them is also around 50% of the maximum rating. These run effectively at room temperature since the Hicap Produces virtually no heat.
In my experience, these units seem to soldier on for decades and I cannot honestly say that I'd noticed any performance degradation to the PSU when using, for example old Chrome case or Olive units in the past. Yet we routinely rip out the caps and replace them.

Two extreme examples there but I'd be interested to hear what others think.

Are we just replacing capacitors in equipment because 'someone' has suggested this is correct, and do people examine the operating condition of capacitors before reaching for the soldering iron?

Is this practice often just another example of following the herd?
 
It is largely bullshit from *certain* manufacturers to make some extra money from you. Amplifiers are not like cars, they don't need servicing unless something goes wrong.
 
Last edited by a moderator:
RobHolt said:
Voltage across them is also around 50% of the maximum rating.
Click to expand...

I though electrolytic capacitors had to be run at near maximum permitted voltage to keep them fit and healthy. If they are not regularly charged up to near their maximum I thought they deformed - I thought the polarising surface degraded.

Maybe I am out of date.
 
You just believed the bullshit.

In this situation a capacitor just behaves like a bit of wire. If it is rated at 5 amp and you put 6 amps or more through it then it gets hot and eventually break down. If you put 1 amps or 5 amps through it (matters not which) then it will run for ever or until the dielectric breaks down or hardens as with old rubber coated cables. 1950's paper in oils in old valve amps are still performing perfectly, as the over spec-ed manufacture made them incredibly reliable.

On that subject we have just lost the last UK paper in oil manufacturer, Ampohm, who has sadly gone bust.
 
Now I feel guilty for replacing all electrolytic caps in my Cyrus 3 last week! It is about 14 years old though.

I think the imaging improved, it always seemed slightly to the right before, now it's dead center. It is just slight though.

I probably could have just replaced the 4x 47uF coupling caps, but I did all of them. Smoothing caps got increased from 7000uF to 10,000uF. Although the old ones said 'long life' on them and use slotted foil. Is it standard practice now to use slotted foil? I'm not sure if the new ones are, lol.
 
Richard Dunn said:
You just believed the bullshit.
Click to expand...

Determining where that stuff is to be found is a difficult business.

I think the Department of Applied Physics and Electronics at Durham University where I was an undergraduate some forty years ago would be unlikely to be dumping such detritus on their students.

Electronic components have improved a good deal over the years, which is why I suggested I might be out of date. I do note, however, that one technical website is referencing the problems I noted, at least for some types of electrolytic capacitors.

Two more Health and Safety pointers relating to electrolytic capacitors:

* Always assume that a capacitor is charged, and seek to discharge it safely before touching it. However, do not short it with a screwdriver ââ'¬â€œ arcing is bad for the tip of the screwdriver, and damages the capacitor.

* When aluminium electrolytic capacitors have lain unused for some time, they may have become sufficiently leaky to break down when voltage is applied, potentially 'dying explosively'. It is possible to 'reform' some capacitor types, by applying an increasing voltage through a constant-current power supply, but this kind of technique is for the serviceman rather than the designer of new equipment.
Click to expand...

http://www.ami.ac.uk/courses/topics/0136_ec/index.html
 
Tenson said:
Now I feel guilty for replacing all electrolytic caps in my Cyrus 3 last week! It is about 14 years old though.
Click to expand...

I wouldn't feel guilty Simon - the Cyrus 3 can run hot and there is no case ventilation. I remember at the Park Inn show you could fry eggs on it!

The slit foil caps are not standard practice. If you want to read up on them, google the work of Morecroft at DNM and also BHC. IIRC the slit foil caps were a joint effort with input from both.
 
As one electrolytic cap of one of my two pairs tube amplifiers (Nestorovic NA-1) didn't work properly (actually it was gone) I changed all the electrolytic caps in all the units.
They were nearly 20 years old and I didn't want to risk to bring each time another unit for repairs. After the change I had the feeling that the stability of the sound image of the one, which was still working, got better. I agreed to put in slightly higher values than the ones before because it wasn't possible to find the exact replacements.

Now I have three pairs of those amplifiers and I thought of doing an experiment:
in each one I have other coupling and decoupling capacitors , which are in the signal path.
So now I have one pair of amps with the "original" ones, the ones which Nestorovic put in in his latest "upgrade" at the end of the 90'.
In the other I have put in the Mundorf Gold/Silver/Oil and in the third one I have the StealthCap from Moncrief.
I think it was a great decision to do this experiment.
I'm really enjoying music at my place more than before.
 
When was the last time anyone saw a paper in oil fail when used within its rated values? or a polyprop, a polyester cap, no me neither just in valve amps.

How many electrolytics have you seen leaky, popped, burst? I've seen lots. Now I don't run Naim amps, but I do like the boxes their Olive and Chrome Bumper kit came in so i have in my time bought quite a selection of older Hicaps and Snaps power supplies from ebay.

It's impossible to over run these, they output 24v, that's it no more no less, they run cool, etc etc, 4 out of 5 that i purchase had one or more of the large electrolytic caps at an advanced stage of failure or had indeed failed, in each case a ruptured lid on the cans with electrolyte oozing out onto the electrodes.

So the requirement to service them regularly may be bullshit, but they do seem to fail somewhere between 10-15 years in normal service in these devices. Or at least the ones they made 10-15 years ago had these lifespans.

Electrolytic caps are just like batteries in that the passage of electrons through them causes a chemical change to take place and as a result they degrade over time.
 
Only once in over 30 years of trading in old nva amps or repairing have I come across leaking caps in nva amps and that was an amp that had been in storage for years and had crusting around the terminals. In that time I have had far more transformers fail.

It is a common delusion to equate capacitors with batteries as they both hold charge. They do not equate, a battery breaks down when it has discharged, a capacitor doesn't. The worst that can happen is a need to reform.
 
Richard there's as much use me telling you about the long term Oxidative chemical degradation of electrolytic capacitors as there was me pointing out that contrary to your beliefs Acrylic was indeed a thermoplastic, or that it indeed shares nothing with glass other than four letters used in a commercial product trade name for the first branded acrylic sheet. Go and do your own research.

I'm glad that you have a spectacularly low failure rate with your caps in your NVA amps, however this doesn't change the fact that those used in the Naim supplies do fail, and with regularity.

It probably highlights the differences in the designs used by yourself and Naim and in the way you both choose to manage inrush current from your transformers and the size of the transformer typically chosen in your amps. Ie Naim typically use heavy and large torroidals (a tiny little) 500VA in the case of a hicap and then don't bother their arse to do anything about inrush current which blows the arse out of their caps.

I don't believe the NAim units fail as a result of the degradation method noted above as that appears to work on significantly longer time scales - you've probably heard of it as 'drying out'.
 
You are talking bollocks and trying to create conflict PER USUAL!!

It has got nothing to do with the size of the transformer, and anyway I am running a pair of monoblocks at the moment with 4300va between them. You seem to forget that capacitors hold residual charge, the only way what you describe could actually have any effect is if the Naim amp totally discharges the caps every time it is switched off. Do you know how long a large cap holds its charge if not deliberately shorted out, obviously not!

Drying out only occurs if the cap or built amplifier is in storage for a long time discharged or that it is being used in a temp environment beyond its spec or a voltage above its spec.

The ONLY reason people say that amplifiers need service is to make money, I presume you are trying to protect you part in that slurp if you are servicing Naim product.
 
Searching again the dark recesses of my memory I find the opinion that in a valve amp a double diode valve rectifier was a better deal than a solid state rectifier because the HT would rise gently to working voltage as the cathode warmed up. With a solid state rectifier the full HT was slammed at the smoothing caps and the rest of the amp.

Maybe it's different now, and I note the best amps run the cathode heaters on DC to reduce mains hum. Is there some clever circuitry the raise the heater voltage slowly to 6.3v so as to extend valve life?
 
Richard, as usual you're in such hate haze you'd rather pick a fight with someone who has just paid you a compliment than read what they actually wrote rather than what you think they wrote.

Naim Hicaps and Snaps are power supplies, not amplifiers. It is these items that have recommended service intervals for their caps.

How long do they hold their charge once switched off you asked? Well about as long as it takes the device upstream of it or the LED on the front of it to drain the power, 10 seconds to a minute max depending on the order of component switch off.

In answer to your question about capacitor discharge, well a disconnected but fully charged large tank cap might hold a charge for many months depending on the temp and humidity of where it is stored. Inside a device, probably quite a bit less.

My job has nothing to do with hifi Richard, i work for a sporting goods manufacturer. So i'm not involved in the slurp, in fact I don't even have to pretend I'm not slurping while shafting my customers by charging greater margins than my competitors.
 
I no longer comunicate with you, it is up to the moderators to deal with you. I do not accept people threatening me, you have made your choice.
 
Have to say I've opened a number of old Naims over the years and have never seen a leaky or otherwise distressed capacitor in a Naim PSU, that includes the pre amp supplies in the smaller power amps. Some were 25+ years old.

I've certainly seen caps go bad on the power amp regulator boards, but that goes back to my initial point, those caps are run under more arduous condition and so fail after about 10 years.
Then again, if they used a higher voltage rated part in the first place.......
 
Agreed a correctly specced part should last decades, not years.

Richard, i believe you have me mistaken with someone else, i've never threatened anyone with anything in my entire life.
 
Just as an interesting point, I received a 3year old Behringer DEQ today that needed fixing. One of the issues was a PSU cap that had leaked. rated 25v and had 9v on it for those 3 years constantly. Poor Chinese parts perhaps, or heat from the pretty hot 7805 next to it?
 

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