2 different types of the same cap in my C-85 - Why?

DWJames

Active Member
I've still got my C4 preamp in a million pieces and struggling to find the time to get it finished, but in the meantime I found a nice C-85 preamp for cheap with only a few little issues, mostly cosmetic or just in need of a minor tweek and blast of Deoxit.

But one of the larger caps is swollen and I'd like to swap it out, but I'm confused...

I have 2 x Nippon 35v 4700uf 85degC caps like this
https://www.dropbox.com/s/k9ska0v89naid2m/2012-11-07 17.30.46.jpg
(note the nice bulging top here)
https://www.dropbox.com/s/otmklkejapye57q/2012-11-07 17.30.02.jpg

and 2 x Elna 35v 4700uf 85degC caps like this
https://www.dropbox.com/s/woj1rvfa6vz6tuk/2012-11-07 17.29.47.jpg

One of each is bulging, so I'll change all 4 out.

They all have the same 4 leads. 2 of which seem to be dummy/mounting leads which go nowhere on the board, so I guess I can swap out for equivalent 2 lead caps with the right spacing, but why are there 2 different types?

Is there any reason why I can't swap all 4 out for the same 35v 4700uf audio grade cap with the right lead spacing or am I missing something here?

thanks in advance,
James
 
i think someone already swapped 2 .or unlikely the factory changed suppliers while it was being made . the one that appears swelling maybe isn't swelling and its just the plastic cover that's expanded .try pressing down on it .
no problem swapping with all same make if you wish .
 
thanks. If I press the top of the swollen one, it springs back as though it's pressurised inside. Is it possible it's just a buildup of gas which I can safely let out by making a tiny hole in the top?
I don't want to change them if I don't have to. I'm just a bit wary after my last Yamaha preamp exploded it's capacitors at me!...
 
its just the plastic cover swelled up a bit ..could be from normal heat from inside or the cap warming up from going bad . not easy to say really . i have big power amps with larger caps that have been fine for years with same looking covers . i think it will be fine but always safer to change for peace of mind .
 
If in doubt ... replace. Long as you're in there, not all that much more work replacing four than two. The swelling or distorted casing usually indicates some level of outgassing, that while not necessarily all that bad, it's worse than good. Could also be the plastic on the sides has shrunk more than the slug on the top, but why mess with it? If nothing else, you end up with a matched set. Caps have changed a LOT over the years as to quality and tolerance.

Discharging caps ain't all that difficult ... just stick yer tongue to them.

Or not. <G>

I'll usually just clip the leads if I can to isolate the cap from the circuit, then put a screwdriver across the leads. Might get a spark doing that, but at least it won't back up into the circuit. You want some real fun, try it with 600v. Whew ... that'll leave a mark!

From there, you can either strip the original lead from the board, or just leave it and use that as an extension for the new cap. Depending on the design that extra wire could be right handy.

PS ... Elna are good caps, but the Nichicon are more than adequate. Your call there.
 
Last edited:
If they push down flat it's just warped plastic from the outer sleeve. Probably nothing wrong with them at all. Is the unit performing correctly?
 
Thanks for that. I'll swap them all out. Easy enough job.

For reference, the current caps are all 35mm diameter, 40mm tall with a 23ish mm lead spacing for the 2 leads that matter.
 
If they push down flat it's just warped plastic from the outer sleeve. Probably nothing wrong with them at all. Is the unit performing correctly?
They're kinda squashy, so you can push them down a bit, but there's resistance as though they're pressurised inside so they bounce back when you stop pressing.

As for performance, silly as it sounds I haven't got that far yet as I don't have the rest of my kit here:rolleyes: I'll know in a couple of days.
 
They're not pressurized, just warped into a dome shape and have some mechanical resistance. Nothing at all to do with the metal can underneath. If the can were bulged you wouldn't be able to push it down. I wouldn't change 'em until everything is either working correctly or you prove there's a problem. If you really don't believe that, cut the edge of the plastic sleeve and slip out the disks so you can check the can. Then put it back. Better yet, put a bridge, cap meter or esr meter on 'em and know for sure. This gotta-change-the-caps disease/FUD gets overdone!
 
They're not pressurized, just warped into a dome shape and have some mechanical resistance. Nothing at all to do with the metal can underneath. If the can were bulged you wouldn't be able to push it down. I wouldn't change 'em until everything is either working correctly or you prove there's a problem. If you really don't believe that, cut the edge of the plastic sleeve and slip out the disks so you can check the can. Then put it back. Better yet, put a bridge, cap meter or esr meter on 'em and know for sure. This gotta-change-the-caps disease/FUD gets overdone!
Thanks, that makes a lot of sense :)
I can see how if they got real hot, the plastic outer casing could shrink and squash the edges of the top plastic disc, forming a dome shape.
So as long as the metal can looks in normal good shape and there's no obvious strangeness in the sound or behaviour of the amp, I should be all good?

Does the outer plastic casing and top plastic disc of the cap serve any purpose other than to electrically insulate the part and provide identifying markings?

thanks,
James
 
Actually it doesn't even take getting very hot. Age and moderate (normal) warmth will do the job. Obviously no one can guarantee they are good without measurement, but if everything is working normally I wouldn't be too concerned. If you have any hum or sound quality problem then I'd look in more detail. The plastic just provides insulation and a more appealing appearance.
 
My C-80 gets pretty toasty during normal usage, and IIRC the C-80 and C-85 are basically identical.
 
All tested now and sounding truly lovely with my valve output converted Marantz cd63, Yamaha PC2002M power amp and Kef 104/2 speakers :)
Very happy indeed with the results for the money spent.

Thanks again for your help guys,
James
 
Back
Top Bottom