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Looking for an unusually large capacitor or a replacement

TGV

May 9, 2013
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Hi. I'm trying to fix an old stereo amplifier (see also https://www.electronicspoint.com/forums/threads/fixing-a-stereo-amplifier.294254/), and I have desoldered the capacitors. That was a bit more difficult than I had expected, but (I think) they all came off without any damage to the PCB.

I had already tried to look up their replacements, but wasn't sure of one pair of capacitors, and now that I've got them off, I still don't know where to get two of the 4700uF/40V capacitors that can be seen in the image. The diameter is 40mm, it has three pins (positive, negative and dummy) and the distance between the pins is 25mm. I can't find any further information on them. I've searched mouser, digikey, alliedelec, future electronics, jameco and a few local stores, but none of them seem to have a single three pin electrolytic capacitor of that size.

Does anyone know if there is a replacement for them? If not, should I simply get a smaller 4700uF/40V capacitor with wire leads? If so, is there any need to secure them to the print board (because I think that's what the third pin is for)?

And about the other capacitors: there's a lot of choice for all of them, but with different ripple current (?) and ESR specifications. Is one choice better than another for audio applications?

Thanks in advance!
 

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davenn

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I still don't know where to get two of the 4700uF/40V capacitors that can be seen in the image. The diameter is 40mm, it has three pins (positive, negative and dummy) and the distance between the pins is 25mm


Just use a standard 4700uF 40V/50 volt cap
modern ones of the same value will be somewhat physically smaller ... no big deal, easier to fit into place :)
 
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WHONOES

May 20, 2017
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Don't know where you are based but, have a look on Farnell's web site. You will probably find what you are looking for on there.
 
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kenny256

Jan 4, 2020
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Did you check it on an LCR meter--is it leaky or did it read nominal values? That would be interesting on a cap from june of 1988.

Nichicon makes large caps with the snap-in terminals in 3- 4- and 5-lead format.
 
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TGV

May 9, 2013
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Thanks for all the answers. I've been digging through Farnell's options thoroughly, I think, but nothing of that size/capacity with three prongs. I guess I'll go with a smaller two-lead one.

And I'm afraid I don't have an LCR meter. Might get a cheap one, when I order.

Thanks again!
 

WHONOES

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A 2 pin device will suffice provided the Pins are of the same pitch and the can is not too large in diameter.
 

TGV

May 9, 2013
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A 2 pin device will suffice provided the Pins are of the same pitch and the can is not too large in diameter.
I can only find caps with wires that fit. There's nothing with 25mm between the pins. Mind you: if it's just two pins, they will be on the center line, and on the old caps they aren't. And there are caps with more than three pins, but they won't fit either. It's a pity, because that huge capacitors with pins have a long lifetime, whereas the best I could find has a 2000hr rating. For a stereo amplifier used daily, that's just a few years.
 

Harald Kapp

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the best I could find has a 2000hr rating.
Don't let that number irritate you. Have a closer look at the conditions under which these 2000 h are valid. With an operating voltage and temperature below the rated value, the capacitor will last much longer.

Where did you search? Using the search term "long life electrolytic capacitor 4700µF" I can immediately find a 4700 µF 40 V capacitor with a lifetime of 12000 h @85 °C. It even has snap-in pins (albeit only 2).
 

TGV

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Sure, but none of them have the pins 25mm apart, as the holes on the PCB are. And the diameter cannot be larger than 30mm in the case of two pins; otherwise, they won't fit. I will look for caps with higher voltage ratings.
 

WHONOES

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Has your old Cap' got a manufacturers name and type number on it?

Edit: Ignore this post. You have a picture in you first post.

See post further on.
 
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TGV

May 9, 2013
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What is it your looking for?
I got a pretty big junkbox!
Two 4700µF/40V/85°C electrolytic capacitors with three snap-in pins (if that's the correct term) at ±25mm distance each, 40mm in diameter, 45mm high. I've attached a picture to my first post. I've ordered smaller ones with longer leads: that should work. But these were made over 30 years ago. Your junk box may be large, but that large?

Thanks for the offer.
 

Martaine2005

May 12, 2015
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If you CAN find a suitable capacitor but the footprint is different, solder the new cap inside the old one. Or add leads to the new cap?.
Quite a common trick for vintage restorers.

Martin
 

davenn

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Two 4700µF/40V/85°C electrolytic capacitors with three snap-in pins (if that's the correct term) at ±25mm distance each, 40mm in diameter, 45mm high. I've attached a picture to my first post. I've ordered smaller ones with longer leads: that should work. But these were made over 30 years ago. Your junk box may be large, but that large?

Thanks for the offer.


Just do as I said way up the thread, the job would have been completed by now and you would be on to something else ;) :)
 

TGV

May 9, 2013
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Did you check it on an LCR meter--is it leaky or did it read nominal values? That would be interesting on a cap from june of 1988.

Nichicon makes large caps with the snap-in terminals in 3- 4- and 5-lead format.
While I'm still waiting on the capacitors (a UPS mess up with wrong delivery and import fees), a quick update to satisfy your curiosity. In the meantime, I did get new multimeter that can measure capacity, and I can tell you that all of the caps have at least the capacity on the specs. Most are near the spec, but one is even 25% above. But the multimeter measures at 3V (I think), not at 34V as the amplifier schematic indicates.

Which makes me wonder: was it the caps after all? Only one way to find out, I guess.
 

kenny256

Jan 4, 2020
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The capacitors appear to be okay. How did you troubleshoot the amplifier to determine that the caps were the culprit?
 

TGV

May 9, 2013
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So there's good news, and bad.

After waiting on UPS to clear up the import duties (I've paid them twice now, and in their system the package is still in some weird state), I got hold of the new caps, soldered them in, check for short circuits, turned it on, and the left channel works (which, TBH, it did before).

So you can guess the bad news: the right channel is dead. I'm going to see if I can find a way to diagnose such a problem. Is there a way which does not involve turning it on? I'm not comfortable with having 220V so nearby. I suspect the only option is testing component by component.
 
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