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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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19th Feb 2020, 2:31 pm | #1 |
Triode
Join Date: Feb 2020
Location: Droitwich, Worcestershire, UK.
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Capacitor replacement old for new
I have a capacitor which is a dark green thing from the 1960s and i need to replace it. finding the size in microfarads is fine however as this is in a car stereo its rated voltage is 12.5vdc whereas the polypropylene version is like 630vdc and i cant find anything lower?? or will this be fine.
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19th Feb 2020, 3:28 pm | #2 |
Dekatron
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Re: Capacitor replacement old for new
What capacity and type is the old capacitor? The 630v will be fine but there may be a more suitable type.
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19th Feb 2020, 3:32 pm | #3 |
Dekatron
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Re: Capacitor replacement old for new
If the capacitor is rated at 12.5VDC and its value is measured in microfarads then it's almost certainly an electrolytic. Their outstanding feature is that for a given capacitance they are physically small. A 630VDC polypropylene should work fine (as long as the circuit doesn't rely on the electrolytic's inherent equivalent series resistance, which it shouldn't). But you might want to check the size. You can buy a 100uF high voltage polyprop https://www.cricklewoodelectronics.c...Capacitor.html. But it will be 110mm long and 58mm diameter and weigh 0.25kg.
Cheers, GJ
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19th Feb 2020, 6:12 pm | #4 |
Triode
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Re: Capacitor replacement old for new
i have attached an image for reference there is only 1 electrolytic highlighted in the manual and this one isnt it.
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19th Feb 2020, 6:55 pm | #5 |
Moderator
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Re: Capacitor replacement old for new
That is a 0.22 uF 125V polyester film 'mustard' capacitor. It is very unlikely to be bad.
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19th Feb 2020, 7:20 pm | #6 | |
Octode
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Re: Capacitor replacement old for new
Quote:
Colin. |
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19th Feb 2020, 8:39 pm | #7 |
Dekatron
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Re: Capacitor replacement old for new
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19th Feb 2020, 9:16 pm | #8 |
Nonode
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Re: Capacitor replacement old for new
But the OP should note that that 0.22 microfarad "mustard" is NOT an electrolytic capacitor.
Any electrolytics likely to have a value of maybe 22 to 2,000 microfarads. Les. |
19th Feb 2020, 10:07 pm | #9 |
Dekatron
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Re: Capacitor replacement old for new
I've found 0,47u electrolytics in older sets, but definitely not 0,22u. I will often replace small value electrolytics (below 2.2u) with polyester or polypropylene capacitors, but this is often impractical for the larger values.
The one in the picture is indeed a Philips polyester capacitor, and they basically live forever. Anyway, I don't understand why the OP includes this picture since he clearly notes it isn't the capacitor in question. |
19th Feb 2020, 11:14 pm | #10 |
Triode
Join Date: Feb 2020
Location: Droitwich, Worcestershire, UK.
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Re: Capacitor replacement old for new
The one in the picture is the one in question. there are several others of the same colour but with different values. There is one electrolytic which stands out rather obvious as it has one end red and one end black to denote the polarity.
Now i have zoomed up i can see it is 125v for some reason i saw a dot in there somewhere. Im just awaiting my capacitance meter to arrive so i can go through and check some of these out. The electrolytic i will more than likely have to replaced. I am only just starting to look at this kind of stuff due to my father buying the car radio for the classic restoration hes doing. i used to do board level repair many years ago on computers, monitors(crt) and PSUs So im very rusty. Now its going to end up as a hobby. The one in the picture is intact but one of the others has chunk missing out of it so im going to need to replace it. |
20th Feb 2020, 12:46 am | #11 |
Dekatron
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Re: Capacitor replacement old for new
Here is a photo showing a mustard capacitor and also one of the less common green spinach ones.
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20th Feb 2020, 7:26 am | #12 |
Dekatron
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Re: Capacitor replacement old for new
In a car radio most or all of the electrolytic caps will be 12v ( though never seen a 12v rated cap) 16v or even 25v. An electrolytic's voltage rating tells you two things, you can't exceed this rating or the cap will die prematurely, also the electrolytic "needs" that voltage across it to keep it formed, IE in good chemical condition.
Your Mullard mustard though can be any voltage within reason as long as it's V rating isn't exceeded. That sort of cap is mostly found in coupling circuits or tone controls, a 63v or 100v rated cap will do here, that being a common rating for film caps in the nanofarad range. Andy.
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20th Feb 2020, 10:11 am | #13 |
Rest in Peace
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Re: Capacitor replacement old for new
I always apply a basic rule, which is that it's fine to use a higher voltage (there may be exceptions) capacitor to replace a lower voltage type, but never the pther way round!
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20th Feb 2020, 10:49 am | #14 |
Dekatron
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Re: Capacitor replacement old for new
For electrolytics it's better not to go too far "over" on the voltage rating just to keep the dielectric insulation happy. Might be a problem if physical size of the replacement is important. (Modern ones can be a lot smaller for the same ratings.)
As has already been said, it's very unlikely that a Mullard "mustard" polyester film capacitor will need to be replaced!
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20th Feb 2020, 12:14 pm | #15 |
Dekatron
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Re: Capacitor replacement old for new
Neither the 'mustard' or the green versions are likely to be faulty. These capacitors have been one of the most reliable ever produced and in a car radio where the maximum voltage is never likely to exceed 14.4 volts (the charging rate) they will never be likely to fail.
Don't waste time checking these....what is the fault on the radio?
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20th Feb 2020, 1:05 pm | #16 | |
Dekatron
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Re: Capacitor replacement old for new
The OP explained in post #10 why he's proposing to replace the mustard (my bold):
Quote:
GJ
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20th Feb 2020, 1:24 pm | #17 |
Triode
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Re: Capacitor replacement old for new
thanks for your help guys and yes i have mustard ones and green ones. just split the volume and control apart and gave it a jolly good clean. so i will be putting that back together.
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20th Feb 2020, 1:31 pm | #18 |
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Re: Capacitor replacement old for new
You mentioned an electrolytic capacitor with red and black ends.
That rings warning bells. It could be a Plessey electrolytic.... one of the LEAST reliable ones known. Most people change these on sight. Red and black plastic ends with a yellow label wrapped round the middle? David
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20th Feb 2020, 3:26 pm | #19 | |
Triode
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Location: Droitwich, Worcestershire, UK.
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Re: Capacitor replacement old for new
Quote:
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20th Feb 2020, 3:45 pm | #20 | |
Dekatron
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Re: Capacitor replacement old for new
Quote:
In case of electrolytics, the capacity may measure fine, or even high but the ESR or the leakage current can be so high it's useless. When the capacity and leakage current are high, sometimes reforming can help. |
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