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Author Topic: Electrolytic Capacitor question?  (Read 2701 times)
KD8ZIF
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Posts: 37




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« on: April 11, 2018, 07:16:07 AM »

Have a question about electrolytic capacitors

I am in need of two 20 uf 350 volt electrolytic capacitors for my Heathkit SB 102, These are radial caps and I have looked around for them on the go to sites like Hayseed Mouser and Digikey but am not finding exactly what I'm looking for?

I am finding 22 uf 350 volt caps but not 20 uf 350 volt caps ?
Can I replace these 20 uf with 22 uf and be ok ?

I did find them in 20 uf with a 450 volt rating and believe they would work in place of the 20 uf 350 volt but wanted to ask before I do it ?

My only concern with the higher voltage 20 uf cap would be physical size ? none of the sites give physical sizes on them so would anyone know it the 450 volt cap would be larger than the 350 volt cap ?

Or am I concerned for nothing due to the fact most modern day caps are smaller than the older caps anyway ?

Thanks

Bob
KD8ZIF
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W8JX
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Posts: 13184




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« Reply #1 on: April 11, 2018, 07:24:06 AM »

Nothing wrong with higher voltage rating, never sub with a lower voltage rating. 22 ufd will work as well
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AA4HA
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Posts: 2623




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« Reply #2 on: April 11, 2018, 07:38:24 AM »

The difference between a 20 uFd and a 22 uFd is 10%, that is the tolerance of most new capacitors. You will have no troubles with this.

Since you are replacing an old electrolytic it was either leaking electrolyte, electrically shorted or the value was so far off it was no longer acting as a capacitor. An old cap of that vintage may of only been down to 2-3 uFd already. Putting in a 22 uFd is going make a significant difference to the power supply.

You are also correct in that the newer caps are usually smaller than vintage components.

One other specification on capacitors that is often overlooked is the temperature rating. If the capacitor is going to be in service in a location where there is quite a bit of heat (from tubes), resistors or transformers you might want to get a cap with a higher temperature rating. It will last longer in that application.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AB4ZT
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Posts: 54




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« Reply #3 on: April 11, 2018, 07:41:22 AM »

Mouser, Digikey - click on "Datasheet" for capacitor in question and dimensions are provided.
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AC2EU
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Posts: 1357


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« Reply #4 on: April 11, 2018, 08:24:22 AM »

It's kind of funny how much smaller the new ones are! You can get close to the same radial footprint but the height is less than a quarter of the originals! I call them "button caps"....
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W8JX
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Posts: 13184




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« Reply #5 on: April 11, 2018, 09:01:39 AM »

It's kind of funny how much smaller the new ones are! You can get close to the same radial footprint but the height is less than a quarter of the originals! I call them "button caps"....

Much better dielectric and plate/foil materials allow thinner materials for a small can with same performance.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
K8AXW
Member

Posts: 6994




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« Reply #6 on: April 11, 2018, 10:54:16 AM »

EU:  When I recapped my SB-200 it took me some time to wrap my ancient head around the much smaller size caps than the ones I took out. 

I kept telling myself "something is wrong here; I'm overlooking something." I spent a lot of time researching this.....for nothing.  A waste of time!  Hd the same problem going from tubes to 3-legged "fuses."
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A Pessimist is Never Disappointed!
KD7RDZI2
Member

Posts: 340




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« Reply #7 on: April 11, 2018, 02:59:00 PM »

I would say that higher voltage rating is better. The difference you meant is really small. New caps are much smaller than once. I had replaced years ago the bias capacitors of a Vintage Drake power supply after checking their ESR and after I was suggested to do so by Garey K4OAH. They were quite smaller and I did glue them to keep them firm.
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WA3SKN
Member

Posts: 6799




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« Reply #8 on: April 11, 2018, 03:26:23 PM »

22 uf and 450 volt will work fine.
The "good old days" specs called for -50 to +150% of value new right out of the box.  You had to buy "computer grade" if you wanted closer specs.  Its amazing how good they have become.
73s.

-Mike.
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N8EKT
Member

Posts: 672




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« Reply #9 on: April 11, 2018, 05:00:13 PM »

22uf will be fine.
Yes, physical size changes with voltage rating.
And different manufacturers have different sizes.
But in most cases especially on older equipment, there is plenty of room for a higher voltage version.
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KD8ZIF
Member

Posts: 37




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« Reply #10 on: April 11, 2018, 08:25:41 PM »

Thanks everyone for all the help, this really helped.
Bob
KD8ZIF
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N4NYY
Member

Posts: 5058




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« Reply #11 on: April 11, 2018, 08:44:12 PM »

Have a question about electrolytic capacitors


I am in need of two 20 uf 350 volt electrolytic capacitors for my Heathkit SB 102, These are radial caps and I have looked around for them on the go to sites like Hayseed Mouser and Digikey but am not finding exactly what I'm looking for?

I am finding 22 uf 350 volt caps but not 20 uf 350 volt caps ?
Can I replace these 20 uf with 22 uf and be ok ?

I did find them in 20 uf with a 450 volt rating and believe they would work in place of the 20 uf 350 volt but wanted to ask before I do it ?

My only concern with the higher voltage 20 uf cap would be physical size ? none of the sites give physical sizes on them so would anyone know it the 450 volt cap would be larger than the 350 volt cap ?

Or am I concerned for nothing due to the fact most modern day caps are smaller than the older caps anyway ?

Thanks

Bob
KD8ZIF

20 uf is an uncommon value and if you find them, they will be expensive. 22uf is a common value and typical replacement for 20 uf.
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KM1H
Member

Posts: 4602




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« Reply #12 on: April 14, 2018, 09:55:02 AM »

20uF was a very common RMA value before the industry changed to 22 and other values followed along with the new RETMA adoption which put all component standards under one umbrella....at least in the USA. Adopted in 1953 but it took many more years for it all to change over. Tolerances today are usually +/- 20%.

Carl
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NO2A
Member

Posts: 1303




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« Reply #13 on: April 14, 2018, 11:15:45 AM »

20uF was a very common RMA value before the industry changed to 22 and other values followed along with the new RETMA adoption which put all component standards under one umbrella....at least in the USA. Adopted in 1953 but it took many more years for it all to change over. Tolerances today are usually +/- 20%.

Carl

Why did the industry change from 3uf to 3.3,or from 5 to 4.7? What was the advantage of doing that? I see these values when recapping my Zenith transistor radios. One oddball
value they had was 40uf,which you can often replace with a 33 that tests at 40. I have seen new 40uf replacements from Newark.
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N7EKU
Member

Posts: 1012




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« Reply #14 on: April 14, 2018, 04:29:00 PM »

https://en.wikipedia.org/wiki/E-series_of_preferred_numbers
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Mark -- N7EKU/VE3
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