Cap - how to test before assembling?

[orson]

I managed to get a nice and huge cap for replacing the third cap in the power supply.
It was cheap because one leg is broken and substituted with copper foil. I will redo the solder joint, does not look good to me.
Now I would like to check the cap for its function before assembling.
I have only a normal multimeter. As far as I understand it a rough test would be: connecting a resistor (value?) in parallel, add a 9V battery to the circuit, measure at the connects of the cap whether it charges, disconnect the battery and see whether it discharges.
Is that right? Or is their an easier way to test the basic function?

[Grainger49]

It is easier than that.  Put your meter on Ohms.  Touch the leads to the capacitor and the resistance will climb. 

After a few seconds swap the meter leads.  You should show negative Ohms and count down to almost zero, then start back with positive ohms and climb.

That charges the cap a little using the battery inside your meter.  When you swap you see the voltage that was charged on the cap as negative Ohms.

[orson]

That sounds good - it is easy enough for me.
And thanks again for the instant response.
I hope that the foil won't cause problems while soldering because of the large surface taking away the heat. I would like to replace it but in this case it seems like the most reliable connection.

[Paul Birkeland]

I would put in a vote not to use that cap for anything beyond a loudspeaker crossover.

The leads coming out of the capacitor are really important for both providing the electrical connection, and for providing a tough mechanical connection to keep the capacitor in place.  I would not expect the foil to last very long on that capacitor, and if it breaks loose on you, you may end up with some unfortunate problems. (Especially depending on where the foil ends up landing)

-PB

[Bonzo]

Me too.
I was once given a very good psu cap without one leg and when I ask my father (a retired hifi technician) what to do with it I was told "trash it".
If removing the copper foil you can see a portion of the leg long enought to solder a wire you could still use it, otherwise return it to the seller.

My two cents, hope you don't mind.

Ciao

[orson]

The cap will be mounted via zip ties attached to a zip tie holders screwed in standoffs. So the leg is not needed to keep the cap in place.
But the foil annoys me as well.
I will desolder the foil and see how much of the leg is left. Looks like there are 2-3mm looking out of the cap. If I can make a solid mechanical connection of a solid core lead to the rest of the leg I would solder this connection and glue the new lead to the cap plus fixing it with a zip tie to the stand off.
I will try this over the weekend and show you a photo of the result and would be happy to hear your opinion on that.

[Doc B.]

I've never been able to make a repair like that hold. To get enough heat into the stub to properly flow the solder onto it for a solid connection you often end up melting the cap. If you try to lighthand it, the cold joint just ends up breaking. If you really have 3mm of the original lead left, bend it in a J and also put a J in the lead you are adding. Hook them together a crimp them. Then solder it up.

[orson]

I disassembled the copper foil - no luck. The remaining leg is about 1mm. No chance to make a solid mechanical connection.
So I burned some money but as mentioned it was not expensive.
I will buy a new one - same manufacturer but rated only at 250 volts. Should be sufficient and is a tad smaller.
Now with the new cap I don't want to break them in with the Crack but before assembling to instantly evaluate the possible change instead of waiting 100 hours not knowing how it sounded before. I found here some posts of Grainger linking to a fast break in for caps. Unfortunately these links are broken. Has anybody a working link to that topic at hand?
The only circuit of breaking in caps I found until now is the one attached.

[JamieMcC]

If you take a sharp knife to the end of the cap and carefully pare away the resin around the stub of the lead out you might be surprised how much lead out can be revealed you don't need much more to accomplish the docs J method

[Paul Birkeland]

I will buy a new one

I will sleep a little better tonight, thank you 

[orson]

JamieMcC - neat trick. Thanks.
Indeed I could create a nice hook that can provide a stable connection.
Let´s see how the soldering works. I will try that tomorrow.

[orson]

I was able to make a good solid connection between the short and the new lead.
They grey stuff is dough glue for car repair - very hard and can take high temperature.
Soldering was not easy with my 40W-iron.
Could definitely look better bit I think it could do the job.
I still have some time to think about it as other upgrades come first, the last cap in the PS will be at the very end.

[JamieMcC]

Have you thought about adding the choke to the power supply at the same time its a inexpensive mod the effects of which are instantly noticeable?

http://uk.mouser.com/ProductDetail/Triad-Magnetics/C-7X/?qs=%2FPiZ59IM4y3T0O8Zu9aP3g%3D%3D

http://bottlehead.com/smf/index.php?topic=6030.0

[orson]

Yes, that is part of the plan.
I thought about the Triad C7X and the Hammond 159M.
The Triad is expensive because of the shipping costs, the Hammond is therefore cheaper to get in Europe.
The Hammond has 259 Ohms and 15 Henries - so even 5 more than the Triad.
But it is a bit larger. So it will be a question of place.

[mcandmar]

Where are you located?    http://www.ebay.co.uk/itm/Triad-C7X-10H-90mA-smoothing-choke-/171093411086?pt=UK_Sound_Vision_Valves_Vacuum_Tubes&hash=item27d5f6450e