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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 4th Dec 2021, 4:02 pm   #1
jmcilkley
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Default Electrolytic Capacitors

Of all the components, electrolytic capacitors are probably the ones with the shortest useful life. Would it not be sensible for manufacturers to put a date code on these items?
When buying new you would be ale to see if they really are new and also when repairing equipment you could easily check the age of capacitors.
I can't see that it would cost the manufacturers anything to do this.
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Old 4th Dec 2021, 4:09 pm   #2
G6Tanuki
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Default Re: Electrolytic Capacitors

In times-past quite a few manufacurers _did_ put a manufacturing-date on the cans of the larger 'smoothing/reservoir' type electrolytics.

With the move to SMD in the last 30 years, the components are often now so small that there's not enough room to put the working-voltage or capacitance on the things, let alone a manufacturer's name or manufactuing date.
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Old 4th Dec 2021, 4:25 pm   #3
kalee20
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Default Re: Electrolytic Capacitors

It's something to take up with the manufacturers, if you are a professional user.

However, I've found that electrolytic capacitors don't generally deteriorate irreversibly in storage, so shelf-life is not an issue. What is the issue, is hours spent at elevated temperatures. But that's not something that can be assessed by date-marks.

(I'm currently listening to a radio built this year, incorporating electrolytics that had been in storage since 1988!)
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Old 4th Dec 2021, 6:11 pm   #4
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Default Re: Electrolytic Capacitors

My experience matches kalee20's.

I believe there was something of a technology change in the 1960's though. Prior to that the electrolytic layer was prone to redissolving into the electrolyte, so capacitors which had sat on the shelf really needed to be reformed before use. More recent capacitors seem to have a much more durable insulating layer and while gently reforming long-stored ones never hurts, it's less likely to be a critical requirement.

As far as cost goes, I think it might be an issue. Manufacturers might find their customers less likely to buy capacitors in bulk if they (the customers) started worrying that they (the capacitors) could go 'out of date' while in stock. Likewise customers might be reluctant to buy capacitors that the manufacturer had been holding in stock, no matter how much the manufacturer reassured them that the date didn't matter much.

Cheers,

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Old 4th Dec 2021, 8:09 pm   #5
whiskas
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Default Re: Electrolytic Capacitors

Just about all of the Japanese capacitor manufacturers date codes their parts with a straightforward four digit YYWW code, or another code which can be easily decoded.
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Old 4th Dec 2021, 10:56 pm   #6
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Default Re: Electrolytic Capacitors

The worst modern capacitors for going out of date are mains filter types. I have never seen one with a date.
They can split and crumble while in stock.
Life is not affected if they used. It is just the same as shelf life.
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Old 5th Dec 2021, 10:55 am   #7
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Default Re: Electrolytic Capacitors

Valves and electrolytic capacitors seems to be the main components with a finite life.

However a capacitor's life is often shortened by the application. Set manufacturers place them next to hot components or in a hot air flow, ripple ratings are often exceeded.

In addition to this, there have been a number of poorly manufactured capacitors over the years. It can't come as any surprise that they become the suspect of many faults.

Contrary to this I recently removed a 100uF 15V plessey (red and black plastic case) from a 1959 TV. Surprisingly it was still measuring close to the original value. I didn't think to check ESR.
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Old 5th Dec 2021, 12:21 pm   #8
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Default Re: Electrolytic Capacitors

I've just measured a Hunts 25uF/25V in a Quad II amp and it comes in at 22.5uF with an ESR of 1.0 ohms. Those results would be perfectly acceptable for a new component. There's no sign of oozing/cracking/swelling of the rubber seal. It's date coded TSD i.e. week 45 1958 which makes it 63 years old. They can fail without warning and quite suddenly though, so I am planning to retire it.

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Old 7th Dec 2021, 7:43 pm   #9
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Default Re: Electrolytic Capacitors

My recently-acquired Heathkit Daystrom RF-1U signal generator was not working when I powered it up. Only the mains indicator neon lamp came on. On opening it up and trying to locate the fault, I found this Plessey 20+20+20 uF electrolytic capacitor to be faulty. The date of manufacture is August 1966. Of the three sections, only one gave a reading of 8 uF. The other two sections did not show any capacitance at all.
I have now replaced it with three new Rubycon 21 uF high ripple 105 C capacitors. This has brought my signal generator back to life.
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Old 7th Dec 2021, 9:20 pm   #10
Lucien Nunes
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Default Re: Electrolytic Capacitors

Of all passives, they have the most diverse behaviours. They can fail hard-short, electrically leaky, physically leaky, high ESR, low capacitance. Some parameters are influenced by age, some by use, most by temperature and some seemingly vary at random or by batch. So a date code, while useful for manufacturing QC purposes, adds little to the understanding of the particular component when dealing with old equipment. Extracting the date code from the cap may tell more about the history of the set as a whole than about the cap itself, unless it shows it to be a replacement.

The other day I replaced a 1958-dated 25μF@25V cathode bypass capacitor that was physically life-expired, with visible electrolyte leakage at the rivet due to a completely perished bung. But even now, it is electrically near perfect, with <0.2Ω ESR, <10μA of leakage and 27μF capacitance. There are many perfect-looking caps with dates this side of the millennium that are completely defunct after a few years' operation near rated max temp. In both cases experience of the parts and their working conditions will better predict the measured performance than date and appearance combined.

I am continually pleased with results from reforming large HV reservoir / smoother cans. It is quite a while since I had one that would not come up. I brought a Bush DAC10 back online only yesterday, no idea how long since it was used but the dual can is spot-on in all parameters. I reform gently and test comprehensively, never leaving it to luck.

Is it my imagination or are German-made etched-foil (i.e. Elko-rauh) caps in the 16-63V range from the 1970s/80s especially prone to hard shorts?
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Old 7th Dec 2021, 9:32 pm   #11
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Default Re: Electrolytic Capacitors

Quote:
Originally Posted by Lucien Nunes View Post
O There are many perfect-looking caps with dates this side of the millennium that are completely defunct after a few years' operation near rated max temp.
Agree. Had a couple very recently in a DAB clock radio (Philips branded) that can't have been that old given the DAB feature. No bulge in the top, no leakage. Maybe the bottom seal was a bit bulged once removed. A component tester measure one as pF capacitor, the other as a pair of diodes. Replacement fixed the issue (mains hum). It was only a hunch given their place in the power supply circuit that made me pull them and test them.
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Old 7th Dec 2021, 11:18 pm   #12
Gabe001
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Default Re: Electrolytic Capacitors

Just wanted to ask, is there any advantage to using large dual electrolytic cans eg the JJs sold by BVWS, over two much smaller separate caps of equivalent value from a reputable brand e.g Rubycon? Does size convey any specific advantage eg ripple current?
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Old 7th Dec 2021, 11:29 pm   #13
Lucien Nunes
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Default Re: Electrolytic Capacitors

Large size does usually imply high ripple capability, yes. The current density in the element is lower and the cooling surface is larger. However, high performance wire-ended types both radial and axial can increasingly match the large cans for ripple spec, especially the 105° types. With a large-format cap you can generally assume it will work in most reasonable valve circuits for which its rating is applicable. For PCB-mount types one does need to check the specs.

Where an existing chassis-mounted HT can is irretrievable, unless an identical replacement is avaiable I tend to leave it disconnected and fit separate wire-ended caps under the chassis, of the best spec I can justfy. If an equivalent can can be fitted without modification I would do that, more for the 'feel' of it than any technical benefit.
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Old 8th Dec 2021, 7:30 am   #14
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Default Re: Electrolytic Capacitors

Thanks lucien
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