On Monday, November 14, 2016 at 3:36:25 PM UTC-5, John Robertson wrote:
On 201611/14/ 12:20 PM, wrote:
Forgive the top posting but WARNING: if a big honking electrolytic capacitor that is more than 60 years old is rattling when shaken, it is absolutely and irredeemingly, irrevocably TOAST. As are its siblings. Reforming is an exercise in futility, and possibly very dangerous, as if by some chance you do actually reform one (or more) for the moment, and it should fail under actual use, all the work previous would be for naught. **POW**.

Agree on the photoflash caps in any case. However, I suspect that the OEM caps are vastly oversize to make up for their rather slow chemistry.

Peter Wieck
Melrose Park, PA

I hear what you are saying Peter, but those caps are industrial grade
caps, not what you would find in a radio. Agreed the shake test will
tell if they are really bad (no rattles!), however attempting to reform
them is not an exercise in futility unless there are obvious signs of
venting around the rubber plug on the top of the can.

If you have access to an ESR meter that will give you a pretty good idea
of the capacitors condition. We sell the Bob Parker kit (as do others)
and using that with an ohmmeter to see if the low ESR is an actual short
circuit or not will give you a pretty good idea of the condition of
these electrolytic caps.

These would have been photoflash rated caps originally and they were
common in photographic gear from the 50s and on. My dad's architectural
photography studio had many flash boxes that used racks of those caps,
back in the 50s/60s and 70s.

John :-#)#

PS, I forgive the top-posting (ducking)

I keep "that" ESR meter, and it is extremely useful. I also have a neat little cap tester that actually tests caps at full operating voltage (up to 450V, that is). It is quite interesting to see caps that seem to test OK in the short term, but over time start to get *warmer* and *warmer* until that **POW** actually happens. It may take an hour or two... When I find one of these, I will hang it (connected) in a Home Depot bucket outside and wait ;-)

My point is that a capacitor, even half-a-dozen capacitors are usually pretty cheap if measured against the alternative failing at a critical moment. These are not the typical cap found in the typical radio - there is a LOT of energy stuffed inside those beasts. Too many for me to trust a 50+ year old cage for containment.

Peter Wieck
Melrose Park, PA