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Old 25th Jan 2011, 7:59 pm   #1
Rick62008
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Default Is a 47uf a good replacement for a 50uf electrolytic capacitor?

I know it isn't a perfect replacement, but i just recently replace one of those dual electrolytic capacitors in a 1953 radio being the original 50uf\330\340v and the replacements 47uf\400v.
I know that i'm playing safe with the 400v voltage margin, but what about the fact that the newer one is 3uf less than the original cap, am i damaging the radio in anyway?

I couldn't get a 50uf replacement as it doens't seem to be a standard value anymore.
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Old 25th Jan 2011, 8:09 pm   #2
David G4EBT
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Perfectly fine - eletroylitics always had a wide tolerance anyway. You'll find the same thing if you wanted 25uF - a common value for grid bypass capacitors in the output stages of valve radios. The modern equvalent is 22uF. Yes, better to go for the higher working voltage version too.

Best of luck with your restoration.

David
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Old 25th Jan 2011, 8:14 pm   #3
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Smile Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Hi,
No, a 3uF difference doesn't matter at all. The original capacitor probably had a manufacturing tolerance of anything up to 10% anyway, maybe more. 47uF is a preferred value thesedays and won't cause any harm.
Cheers, Pete
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Old 25th Jan 2011, 8:18 pm   #4
AlanBeckett
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Quote:
Originally Posted by Tractorfan View Post
The original capacitor probably had a manufacturing tolerance of anything up to 10% anyway, maybe more.
Many old electrolytics, particularly 'smoothers', typically had a tolerance of -50% +100%.
Alan
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Old 25th Jan 2011, 8:18 pm   #5
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Don't worry about it. The tolerance on electrolytics is usually large, so although it says 47uF or 50uF on the can either of them could easily be 40uF or 60uF in practice. The designer in 1953 would have allowed for this. Things you have to be a bit more careful of include the ripple current rating of the new capacitor. There's a drive to make really small components now and these can sometimes struggle to deal with large ripple currents. But if you go with a decent manufacturer they will usually be able to supply you with a more than adequate ripple rating.

Cheers,

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Old 25th Jan 2011, 8:22 pm   #6
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

FT Cap make the original style ali can capacitors. There is a dealer in Germany, but he is expensive: Google "Ask Jan first". Friendly chap though. He does twistloks too!

http://www.audiocap.co.uk/ft-capacitors-2-c.asp

You need at least 20% headroom when looking at the voltage rating of an electrolytic in a filter circuit. So if your system runs at 300volts, then a rating of 360 volts upwards is fine. As said, 47uF is perfectly fine.

Good luck,
Martin
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Old 25th Jan 2011, 8:23 pm   #7
Rick62008
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Thank you for helping out. This has been hammering in my head for a while because i was afraid i could be damaging the radio in anyway.

Cheers
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Old 25th Jan 2011, 8:28 pm   #8
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Yes perfect. 47uF is the modern 'prefered' value. 3uF will make absolutely no difference whatsoever. Most electrolytics have a very wide tollerence like +50% -20% so don't worry about it. Just for your information, most smoothing capacitors in valve radio's have a range between 4uF to 50uF and the nearest modern 'prefered' values would be

original prefered
4uF 4.7uF
8uF 10uF
16uF No direct so use 10uF in parallel with 4.7uF or use a 22uF*
32uF 33uF
50uF 47uF

*Some rectifier valves are critical of reservoir capacitor values. It is not desirable to choose too high a value for the reservoir. If the 16uF is a smoothing capacitor then there is no harm in using the 22uF.


Hope this helps.



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Old 25th Jan 2011, 8:36 pm   #9
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

It does thanks. By the way, is 25uf a standard value today? If it is, i could have coupled them in parallel. Anyway, as all of you said this will do just fine!
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Old 26th Jan 2011, 12:34 am   #10
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Quote:
Originally Posted by Rick62008 View Post
By the way, is 25uf a standard value today?
No you'll find it's 22uF.

Capacitor replacement is not a problem for most values because you can series or parallel modern caps as required although you should use balancing resistors if you series them.


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Old 26th Jan 2011, 10:38 pm   #11
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Quote:
Originally Posted by Sideband
16uF No direct so use 10uF in parallel with 4.7uF or use a 22uF*
15uF caps are available.

http://uk.rs-online.com/web/search/s...chTerm=5262310
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Old 26th Jan 2011, 11:42 pm   #12
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

Yes 15uF are available but suppliers like CPC/Farnell don't seem to stock them in high voltages...haven't looked recently but I have had difficulty getting 15uF types in 350...400V range. 10uF and 4.7uF in the 250V to 450V range seem to be available by the bucketload however.




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Old 27th Jan 2011, 2:45 pm   #13
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Default Re: Is a 47uf a good replacement for a 50uf electrolytic capacitor?

I have used 47uf radial electrolytic capacitors to fix 50uf smoothing capacitors but have always stuffed them in the original can.

I keep all the high voltage axial capacitors in the values mentionned above, and recently have bought some from Studio Electronics in Burbank California where they are very reasonably priced. They stock 4uf, 8uf, 10uf, 16uf, 20uf, 22uf, 33uf, 40uf, 47uf, 50uf and 100uf 350v, 450v or 600v MIEC (Taiwan) branded electrolytic axials eg: 20 x 450v 8uf cost $20 (£12.50) + £8.50 p&p which works out at £1.05 apiece. Most of those values are not available in the UK, although Audiocap do one or two German 450v F&T axials. Audiocap will no doubt be at the forthcoming Tonbridge Audiojumble, it's well worth a visit to their table.

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