[Milsurplus] Capacitor issues

[Kenneth G. Gordon]

On 2 Jun 2016 at 12:54, Ray Fantini wrote:

>     So a 1936 USCG R-104 receiver followed me home from Dayton, it´s very clean and in no way 
>     modified and the intent is to build an external power supply and case and have it working. One 
>     of the problems is that it uses two huge square 4 mfd @400 volt capacitors in its power supply 
>     input along with a filter choke and both of the capacitors have leaked a lot of oil out of the can 
>     and all over the chassis.

In my experience, those oil-filled caps, unless they are leaking oil, are pretty much always 
good.

> In the picture you can see one of the offending capacitors that´s been 
>     removed and cleaned up but I don´t want to put it back in being it will just leak more oil over 
>     time.  It still checks good with only a small amount of leakage but would not trust it anyway. So 
>     the big question is what´s the best way to open this up and remove the guts and substitute the 
>     innards with a modern capacitor? It appears that the original can is soldered all around but I 
>     would prefer to keep the original external appearance and finish being everything in the radio 
>     matches so heating this up with a torch would be issues also don´t know if the oil is flammable. 

Again, in my experience, the oil (PCB) is not flammable, at least at soldering temperatures. 
Also, in the small quantities contained in such capacitors, it is not toxic as long as you wash 
your hands after handling it. Instructions I have received from Environmental Agencies is to 
simply throw it away if you wish.

>     Maybe the answer is cutting around the base of the can but at this point have no idea on how? 
>     maybe a dermal tool with a cutting wheel?

That would work, although you would get oil all over.

> Is it possible that if the base of the can is heated with 
>     a torch that the entire contents can be dropped out?

Except for the connections at the "top", yes.

> Another option may be to solder up the 
>     small hole on the outside of the capacitors can and install it back and keep it original?

That would also work. In fact, all the oil-filled caps I have here have a "solder blob" on the 
outside of the can. I always assumed that was where the oil was inserted. If your solder blob 
is missing, leaving a hole, then solder it up and test the cap.

> Have lots 
>     of questions but no answers at this point. In the past I would have just replaced the offending 
>     parts with modern ones but in this case wanted to keep the receiver looking the same so that´s 
>     the source of the dilemma.

Yes. We understand.

The first question I would ask is "How much oil has leaked out?", if you can tell. If most of 
the oil is still in the cap, then soldering up the hole, cleaning up the mess, and reinstalling 
the cap would be my first inclination.

If a lot of the oil has leaked out, I would then consider carefully opening the can and 
installing a modern, high-quality, replacement, closing the can back up with either solder or 
epoxy, repainting it and reinstalling it. I'd use solder if grounding the can is important, but 
epoxy if that isn't a factor. JB Weld is good stuff.

Ken W7EKB