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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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5th Nov 2020, 3:00 pm | #1 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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WIMA [not Rifa] capacitors.
I've got these WIMA capacitors - 0.47uf 400VDC - which _look_ somewhat like the Rifas we know-and-hate.
I was planning to use them for things like screen-grid and cathode-decoupling in RF circuits where the maximum HT will be around 250V. Should I risk it? Or should I throw them in the bin and fit nice new yellow MKT capacitors instead? |
5th Nov 2020, 3:06 pm | #2 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
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Re: WIMA [not Rifa] capacitors.
I think these are mixed dielectric caps, if so I would bin them, unless of course anyone know different.
Duolit or something similar jogs my memory, I used them in the 1970’s.
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Frank |
5th Nov 2020, 3:28 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: WIMA [not Rifa] capacitors.
I am inclined to bin them, on the basis that I've got loads of new Vishay MKT in stock and it doesn't make sense to fit possibly-suspect parts when known-good ones are available.
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5th Nov 2020, 3:33 pm | #4 |
Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,958
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Re: WIMA [not Rifa] capacitors.
I have found that the TFF or TFM (Tropyfol F or M) dielectric capacitors to be pretty good compared to the older dark brown lozenge shaped ones. I agree with Nuvistor that the Wima Duolit mixed dielectric capacitors are not very good these days.
Ron |
5th Nov 2020, 3:35 pm | #5 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: WIMA [not Rifa] capacitors.
Those look like Wima Tropyfols, one of the early plastic film types and nearly as high in the esteem stakes as Mullard mustards. High-quality vintage Continental audio kit bristles with the things and, closer to home, both my 5-20 and AR88 have coped with them for nearly three decades.
If you don't like them, you could always stick 'em on eBay |
5th Nov 2020, 4:48 pm | #6 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: WIMA [not Rifa] capacitors.
My fairly limited experience of these in Grundig tape recorders is that they are very good, also see:-
https://www.vintage-radio.net/forum/...d.php?t=171868 David |
5th Nov 2020, 4:54 pm | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: WIMA [not Rifa] capacitors.
Maybe I won't bin them after all; who knows - they may appreciate in value enough to buy me a small tropical island by 2050!
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5th Nov 2020, 5:31 pm | #8 |
Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,958
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Re: WIMA [not Rifa] capacitors.
Maybe a small Tropyfol island!
Ron |
5th Nov 2020, 5:36 pm | #9 |
Octode
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,030
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Re: WIMA [not Rifa] capacitors.
I have a lot of red cased Wima caps. Are they any good?
I got them from work when there was a clear-out of unused stock so they must be all of 30 years old by now! |
5th Nov 2020, 5:48 pm | #10 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: WIMA [not Rifa] capacitors.
No experience of these but as they are MKS a Metalised Polyester (PET) I would expect that they (even though old) may well be OK, I would try checking some out for capacitance and ESR measurements.
David |
5th Nov 2020, 6:19 pm | #11 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
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Re: WIMA [not Rifa] capacitors.
I've got some, too. And right now, playing beside me, is a GEC BC5842 which has a couple in, replacing the original waxies, 32 years ago.
They're epoxy moulded, with unfilled resin. So occasionally I have seen cracks. But the capacitor element is polyester, which unlike the dreaded metallised paper Rifas, does not absorb moisture, swell, go leaky, and generally do undesirable things. I'd do 'standard' measurements as David above advises - but I'd have no worries about using them. |
5th Nov 2020, 6:59 pm | #12 |
Octode
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,030
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Re: WIMA [not Rifa] capacitors.
Thanks.
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5th Nov 2020, 7:35 pm | #13 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,385
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Re: WIMA [not Rifa] capacitors.
The colourful stripey Mullard C280 series polyesters are chronic shedders of their outer coating, often leaving the foil exposed, yet seem to soldier on. I've seen examples in hot, hard-working applications like monitor scan circuits where the crunchy coating is almost entirely missing but they still seem to be working away. There's a series of polycarbonate capacitors (forget the designation) that are completely uncoated yet do their job fine (apart from the standard supplier warning about exposed live foil and terminations) and are widely used in applications like audio filters that demand consistency and stability. It's pretty impressive just how good some.plastic dielectrics seem to be.
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5th Nov 2020, 8:02 pm | #14 |
Octode
Join Date: May 2003
Location: Belper Derbyshire
Posts: 1,910
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Re: WIMA [not Rifa] capacitors.
I would stick those 400V rated capacitors across say a 1000V hand cranked megger and see if there is any leakage at this pressure. If they survive this without any leakage then they should be ok in circuits rated at less than 400 V. Also check if their capacitance and ESR if known is within tolerance.
Christopher Capener
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Interests in the collection and restoration of Tefifon players and 405 line television |
5th Nov 2020, 10:28 pm | #15 |
Hexode
Join Date: Dec 2019
Location: Hohenroda, Eastern Hesse, Germany
Posts: 453
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Re: WIMA [not Rifa] capacitors.
Hello,
I have met those WIMA Durolit capacitors frequently in German made sets. I suggest to replace them all. MKTs are okay as well as Tropyfoil. Regards, Joe |
6th Nov 2020, 12:25 am | #16 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: WIMA [not Rifa] capacitors.
Have not heard of Durolit before, looking at some images of them they look very similar to the Tropyfol, luckily the Durolit ones say Durolit on them (at least on the images I looked at).
David |