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Old 18th Sep 2019, 9:09 pm   #1
poppydog
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Default Capacitor restuffing issue.

I need to restuff a 50+50uf smoothing electrolytic as its very bad, I have some issues though. I purchased these rubycons to go inside of the original can but I didn’t do my maths properly and they wont fit inside the can side by side as they are slightly too big.
https://uk.rs-online.com/web/p/alumi...d%22%3Atrue%7D

I hastily ordered some slimmer NIC caps, this time checking dimensions etc and noting it said high ripple current in the description. After actually reading the ripple current rating (after I had ordered it) it appears these may not be suitable, another cock up. Can any body tell me if there is a possibility I just might be able to use these being such a low value cap?
https://uk.rs-online.com/web/p/alumi...d%22%3Atrue%7D

If not how can I get the rubycons in there? I was thinking maybe a tier type set up but I would need to add a couple of inches to the leadouts of the uppermost cap, some research tells me its not a good idea to lengthen the leadouts.
There really isn’t room to put them underneath chassis as its pretty tight around the tuning cap plus Id like them not to be seen really. I could buy a ready made dual cap but they are expensive the wrong colour and I would have the headache of how to mount it plus the ferrite is mounted on top of the original can.
The cap I need to stuff is c57/c58 on the sheet, link below

https://www.doctsf.com/documents/aff...1209&num_fic=1

Regards Poppydog
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Old 18th Sep 2019, 9:15 pm   #2
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Default Re: cap restuffing issue

Looks like the ripple current on the RS page is a misprint and should read 0.44A, not mA. Look at the manuf data sheet to confirm.

Ken
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Old 18th Sep 2019, 9:44 pm   #3
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Default Re: cap restuffing issue

The allowed ripple is indeed 440mA @120Hz. That seems good enough. I would probably choose the 10mm diameter version, 450mA ripple current and a better chance of fitting 2 in the old can. Never forget to use shrink sleeves as the factory fitted sleeves are not rated for insulation purposes.
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Old 18th Sep 2019, 10:25 pm   #4
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Default Re: cap restuffing issue

If you have been looking at how I did them from under the chassis by drilling through the bung then the part I used is made by Rubycon and is sold by Farnell.
They are 10mm diameter.
https://uk.farnell.com/rubycon/400bx...-20/dp/2342034
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Old 19th Sep 2019, 9:35 am   #5
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Default Re: cap restuffing issue

Can lengthening the leads to an HT smoothing capacitor by a couple of inches really make any difference?

Andy
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Old 19th Sep 2019, 10:04 am   #6
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Default Re: cap restuffing issue

Data sheets for the chosen capacitor....ripple frequency correction factor tables at the bottom of the last sheet:

https://docs-emea.rs-online.com/webd...6b81131801.pdf

I get the second but not the first....?

Lawrence.
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Old 19th Sep 2019, 10:23 am   #7
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Default Re: cap restuffing issue

Quote:
Originally Posted by M0FYA Andy View Post
Can lengthening the leads to an HT smoothing capacitor by a couple of inches really make any difference?

Andy
I was a little puzzled by that, too- I can see that adding a couple of inches to a decoupler in a VHF tunerhead would be unwise, also doing so in the case of a reservoir capacitor in a high current, high frequency, low voltage SMPSU could detract from its full potential effectiveness, but with a modest valve radio where a few tens of milliamps of HT are involved with 50/100Hz ripple a bit of perspective is needed. When re-stuffing a filter block for an AR88, I extended the leads on the replacement innards to reach to the original block terminals- but they were nothing like as long and spindly as the original internal connections! The trouble with info from the 'net (in particular) is that there's a fair amount of didactic nonsense that needs to be sifted from the genuinely useful tips, and it's all too frequently presented without realistic context or sense of proportion,

Colin
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Old 19th Sep 2019, 11:37 am   #8
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Default Re: Capacitor restuffing issue.

Adding a couple of inches of wire at mains related frequencies will simply increase the ESR a bit. For two bits of 1mm dia wire, two inches long it's about two milliohms. At 400mA ripple current that's about 800uV of extra ripple voltage. Meh!

Just use the longer leads on the smoothing cap rather than the reservoir.....
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Old 19th Sep 2019, 8:19 pm   #9
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Default Re: Capacitor restuffing issue.

Thanks for all the replies, its good to know I can use the NIC ones if need be, being Japanese I would imagine they should be ok.

With regards to Martens comment on using heatshrink tubing round the outside of the caps, would that affect the cooling of the caps? You also see caps being restuffed with gallons of hot melt glue holding everything together, surely that must affect the cooling?

Turretslugs comment regarding the "didactic nonsense" needing to be sifted is true.
I typed on google "can I extend capacitor leads" the first result you see is from this forum
https://www.vintage-radio.net/forum/...d.php?t=106515

I read Chris's reply to the thread back in 2014 and decided not to look any further, hence my comment..

regards poppydog
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Old 19th Sep 2019, 8:35 pm   #10
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Default Re: Capacitor restuffing issue.

I don't really think that with modern electrolytics you should be worried about cooling. OK, in days-gone-by when electrolytics were not much more than a couple of bits of silver-foil dipped in lye, they got hot both because of series-resistance and leakage - but those days are thankfully long gone - now we have distinctly-impressive 'electrolyte' formulations and computer-controlled etching of the foils before assembly.

I worry more about electrolytics gaining-heat from surrounding things like heatsinks/resistors/valves than any issues of internally-generated heat.
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Old 20th Sep 2019, 12:07 am   #11
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Default Re: Capacitor restuffing issue.

I certainly re-stuff capacitors when the canisters have a unique shape & size and fitting or chassis hole, where I want it to look original and not modify the chassis.

However, much of the time this is not necessary now as many new reproduction can style capacitors are available for vintage radio/TV restoration and it is much more cost effective and professional result is obtained from fitting these instead.

If you posted a photo of you capacitor with its dimensions, I might be able to advise a source for a new replacement, it depends on the particular type.
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Old 20th Sep 2019, 1:59 am   #12
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Default Re: Capacitor restuffing issue.

It can be worth making an isolated negative terminal lead for the first 50uF filter cap, which would connect directly to the power transformer CT, and constrain the biggest charging currents to just that isolated wire. That first negative terminal can be connected to the second cap negative terminal, and that terminal then connected to the can rim that is being connected externally to 0V or chassis.
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Old 20th Sep 2019, 6:03 am   #13
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Default Re: Capacitor restuffing issue.

I wouldn't worry about increasing the length of leadout by a few inches or so. I've done it many times without issue and the ESR of capacitors is not so critical with valve equipment....in fact I doubt it was even thought about back in 'the day'. In a switch mode power supply running at 10's of kilohertz, ESR becomes critical. At 50 or 100Hz in valve equipment a few extra milliohms can be ignored.

Maybe in a high quality valve power amplifier where earth currents can be critical you'd have to be more careful....perhaps......
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Old 20th Sep 2019, 7:20 pm   #14
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Default Re: cap restuffing issue

Quote:
Originally Posted by ms660 View Post
Data sheets for the chosen capacitor....ripple frequency correction factor tables at the bottom of the last sheet:

https://docs-emea.rs-online.com/webd...6b81131801.pdf

I get the second but not the first....?
The first table is for the below 160V types. They use another electrolyte and/or another internal construction.
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Old 20th Sep 2019, 7:49 pm   #15
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Default Re: cap restuffing issue

Quote:
Originally Posted by Maarten View Post
Quote:
Originally Posted by ms660 View Post
Data sheets for the chosen capacitor....ripple frequency correction factor tables at the bottom of the last sheet:

https://docs-emea.rs-online.com/webd...6b81131801.pdf

I get the second but not the first....?
The first table is for the below 160V types. They use another electrolyte and/or another internal construction.

I still don't follow, eg: 10mmx30mm 820uF @ 35 volts shows a ripple current rating of 1.48 amps @ 120Hz ?

Lawrence.
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Old 21st Sep 2019, 12:14 am   #16
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Default Re: Capacitor restuffing issue.

Quote:
Originally Posted by poppydog View Post
Turretslugs comment regarding the "didactic nonsense" needing to be sifted is true.
poppydog
With anything involved in filter electros on power supply systems in (most) vintage valve gear, often the manufacturers placed the electrolytics on the chassis in places suited to their physical mounting and appearance, with no regard to the location of the circuitry they were connected to. Especially, for example mutli-units with many capacitors in the one canister. The wiring simply ran from those anywhere in the circuit(could be on the opposite side of the chassis). Sometimes though the canisters are placed where they are purely so the lugs can be used as a mechanical tie points for wires & components to save money on extra tag strips.

This is because even three feet of wire has an insignificant resistance and inductance compared to the internal properties of the actual electrolytic capacitor. Where there are any concerns about that circuit point being RF tight, simply at the other end of the wire something like a 0.1uF cap would bypass the connection to ground. Most of the time, unless it is a part of the circuit processing RF, they would not bother with that either.

So you certainly don't need to worry about wire lengths leading to your power supply filter electros and if there are any circuits powered by those voltage rails, that required a RF bypass cap to ground, the capacitor will already be there.

You might see some remarks about wiring length, earth points where people are fanatical about it in the audiophile industry, and while, like most good jokes, there is always an element of truth in it, they concentrate on the external wiring and do not realize that the small changes they make there are mostly dwarfed by the internal electrical properties of the electrolytic capacitor itself. In fact, if most of the makers of audio equipment really understood how bad these are a lot of the time, they would splash out and use large sized super low ESR non electrolytics which have an internal construction with the lead wires welded to their foils and consign the electrolytics to the trash can where they most probably belong. And with these sorts of non electrolytic capacitor designs you seldom would worry about ripple current ratings, because the losses inside the capacitor are negligible and little heat is generated.

I have attached a photo of the types of non electrolytic capacitors I use in my restorations now, because I became sick & tired of troubles caused by electroltyics.
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Last edited by Argus25; 21st Sep 2019 at 12:30 am.
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Old 21st Sep 2019, 10:40 am   #17
Maarten
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Default Re: cap restuffing issue

Quote:
Originally Posted by ms660 View Post
Quote:
Originally Posted by Maarten View Post
The first table is for the below 160V types. They use another electrolyte and/or another internal construction.

I still don't follow, eg: 10mmx30mm 820uF @ 35 volts shows a ripple current rating of 1.48 amps @ 120Hz ?
I now see the problem as well. I would think from the first table that lower voltage electrolytics are actually specified at 10kHz so you'd have to apply the 0.6 factor to obtain the 120Hz max. current, as opposed to what it says in the lookup table. On the other hand, it could mean that it can withstand a still greater current at 10kHz.
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Old 24th Sep 2019, 9:41 pm   #18
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Default Re: Capacitor restuffing issue.

Thanks for all the replies, I will let you know how I get on.
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