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Old 13th Oct 2021, 12:28 pm   #1
6SN7WGTB
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Default RIFA X2Y cap - would appreciate views

I see the exploding RIFA thread is closed, so afraid I need to open a new one.

I would appreciate views on the one shown below - I have a stock of them and have been using them for some while without issue, but of course the potential breakdown will creep up.

FYI, they are ex-RS part number 239-668.

The date code is September 2002.
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Old 13th Oct 2021, 12:37 pm   #2
Maarten
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Default Re: RIFA X2Y cap - would appreciate views

If they were stocked at a constant temperature and low humidity, they'll probably be good a few more years. Otherwise and after that, they will prevent views by laying a smokescreen as they do.
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Old 13th Oct 2021, 12:41 pm   #3
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Default Re: RIFA X2Y cap - would appreciate views

They look just like the hard-epoxy Rifa capacitors that Ive had trouble with!

I'd be happy using for a short-lived bench prototype, if pushed - but not for anything expected to be still working in 10 years time.

How they've been stored is important - out of sunlight, and in a dry environment, is best.
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Old 13th Oct 2021, 12:41 pm   #4
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Default Re: RIFA X2Y cap - would appreciate views

Personally I'd throw them out. No virtue in fitting components which will inevitably fail at some point.

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Old 13th Oct 2021, 12:57 pm   #5
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Default Re: RIFA X2Y cap - would appreciate views

All stored in their original sealed bag in a box in an indoor room temp cupboard.

These are still sold by RS (under the same part number) - so is the consensus that even a new one is a high risk? I'm struggling a bit with that...

So what would be (less un)reliable alternative(s)?
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Old 13th Oct 2021, 1:39 pm   #6
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Default Re: RIFA X2Y cap - would appreciate views

The basic principle of construction (potted impregnated paper) is flawed (antiquated, replaced by 1960 for most applications and by 1990 for all other applications, not at the right price point to make ones that last, etc.) and the execution is mediocre at best. Most X capacitors will fail at some point through wear and tear, but modern plastic foil ones will at least degrade gracefully and usually only with use, not with time. Any MKP (metallised polypropylene foil) replacement will be better, though quality may vary a bit by manufacturer.

The rationalisation for such MP capacitors to still be produced might be their past marketing still deceiving some people (RIFA was especially infamous for touting their superiority) and a conservative customer base (including NATO stock probably, retrofitting modern types might be expensive administratively).

In the past, even up into the 1980's, they did fit a niche market for mains filters and RC-suppression circuits. Polypropylene was not yet cheap and reliable enough and the alternative was mixed dielectric (paper+polyester) which was only slightly more reliable. It was easy to import equipment fitted or retrofitted with those capacitors to pass local inspections, hence probably their marketing.

P.S. The use as Y-capacitors in non-earthed equipment is especially dangerous as they might go leaky without warning.
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Old 13th Oct 2021, 1:51 pm   #7
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Default Re: RIFA X2Y cap - would appreciate views

At least the potting on the one shown is not cracking so it might be OK for a few years. Any that show cracking of the potting should be treated with great suspicion since they are likely to have absorbed moisture.
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Old 13th Oct 2021, 3:32 pm   #8
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Default Re: RIFA X2Y cap - would appreciate views

Is it just me? There appears to be a couple of tiny cracks across the text "40\1....“ in the first picture, if the type PZB is metallised paper based and they looked like that, I wouldn't use them myself.
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Old 13th Oct 2021, 3:39 pm   #9
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Default Re: RIFA X2Y cap - would appreciate views

No cracks at all - looked via a loupe to be sure. I think the strong sunlight reflecting off of the foil printed liner - which is very lined in itself - make sit look like the case may have fine cracks.

Funny about paper caps - if I found one in some valve gear, it would be straight out and into the bin...

Has anyone found any relationship between insulation resistance and/or leakage and life expectancy?
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Old 14th Oct 2021, 4:30 pm   #10
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Default Re: RIFA X2Y cap - would appreciate views

Quote:
Originally Posted by ajgriff View Post
Personally I'd throw them out. No virtue in fitting components which will inevitably fail at some point.

Alan
I don't why, but sooner rather than later, unless a 250V part at 12V, they either burn or go bang.
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Old 14th Oct 2021, 5:34 pm   #11
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Default Re: RIFA X2Y cap - would appreciate views

Just tested them with a Megger at 500V and 1000V: >50MΩ.

BUT put one across the mains and leakage = 8mA, which is a lot.

To be precise, this was measured in the Live conductor fed from a isotran with no secondary earth - so this is all L-N (thru either X2 and/or the Y2s) and so I couldn't say what's going down the earth thru just the Y2s in normal use. No reason to assume it isn't in line with this.

Tests closely in any of three of that batch.

Looking at the values, I'd expect a reactance in the MΩ range at 50Hz, but I'm clearly seeing tens of kΩ instead.

Unless I'm missing something?

Bin it is. Potential for nuisance RCD trips here.
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Old 14th Oct 2021, 5:55 pm   #12
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Default Re: RIFA X2Y cap - would appreciate views

RS 239-668:

https://docs.rs-online.com/de41/0900766b81717876.pdf



https://www.electronics2000.co.uk/ca...calculator.php

Which at 245VAC would be near as damn it 8mA.

Lawrence.

Last edited by ms660; 14th Oct 2021 at 6:07 pm. Reason: extra info
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Old 14th Oct 2021, 6:11 pm   #13
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Default Re: RIFA X2Y cap - would appreciate views

I would throw them away and you won't have to worry about them.
As others have said, the likelihood of failure is too high to warrant using them and saving a little bit of money. They could potentially do very costly damage. In my opinion, it's just not worth the risk...
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Old 14th Oct 2021, 6:26 pm   #14
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Default Re: RIFA X2Y cap - would appreciate views

You could downgrade them and use them for different applications. Personally I'd be happy to use them as HT decouplers in typical valve radios, and of course in low voltage circuits, though they're a bit physically big for that.
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Old 14th Oct 2021, 6:27 pm   #15
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Default Re: RIFA X2Y cap - would appreciate views

Quote:
Originally Posted by ms660 View Post
You're exactly right.

I don't know how I mis-calculated that as I indeed used Xc = 1/(2PifC).

Oops.
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Old 14th Oct 2021, 6:29 pm   #16
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Default Re: RIFA X2Y cap - would appreciate views

I see KEMET do a 100R and 100nF in series suppressor cap - or 'snubber' I suppose we might say.

It's paper yet again, but of different build.

https://docs.rs-online.com/e1d2/0900766b809c6e10.pdf
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Old 14th Oct 2021, 6:39 pm   #17
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Default Re: RIFA X2Y cap - would appreciate views

Do not hesitate - throw them out. Save yourself pain, grief and acrid smoke.
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Old 14th Oct 2021, 6:45 pm   #18
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Default Re: RIFA X2Y cap - would appreciate views

Good to see you've decided to consign them to the skip: I never really understand why "NOS" parts that have undergone decades of ageing while sitting on a shelf somewhere are treated with such reverence [specially by the audiophools].

New parts are cheap [when you look at how many minutes even a minimum-wage worker would need to earn the cost of a new part compared to what they would have to have worked to buy an equivalent part in the 50s/60s/70s/80s].

These days the time/labour-cost of fitting a part often exceeds the cost of the part itself... so it makes sense to fit only the best-quality parts.
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Old 15th Oct 2021, 8:42 am   #19
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Default Re: RIFA X2Y cap - would appreciate views

Agree re best quality. Sadly our industry is swamped with low quality parts from you-know-where, but weeding out these sorts of duffers from more respected providers is almost more frustrating!

I always use Vishay VR25/37 resistors for bleeders across mains caps - another place where an unexpected pop isn't very desirable!
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