arvin chaissis cleanup gone wrong!

[miniman82]

I don't have the fancy machine, so when I need to test here's what I do.

I have a chassis which only contains a transformer and a 5U4 rectifier tube, whose output goes through a small value resistor. With the chassis on a variac, I connect a test cap to the output side of the resistor and ground. Each time you increase input voltage to the chassis with the variac, you will notice that the reading on a meter placed across the resistor increases slightly than settles down as the cap charges. If you have a bad one, the reading will go up and up and the resistor will get very hot. Very old caps sometimes take a very long time to reform, some can't be saved at all. I've found that it's not the initial charge that is the deciding factor in a cap surviving at all, rather it's ability to stay formed is what counts.

For example, say you get an old cap reformed. Leave it on a shelf discharged for a week, then repeat the same test. Chances are you will have to reform it again, because it's simply too old to work anymore. Dry electrolyte, corroded plates, ect. You will notice that you have to wait and wait for the meter reading to come down before you can apply more power, and the cap should be tossed.

Some caps hold form just fine, especially if they come from the NOS pile. I've had pretty good luck charging caps this way, last set I did was a pair of old Sprague cans. Rated voltage on them was 450, and they were 250uf per section. It took me about a half hour, but they formed great and even held up at 525 volts with minimal leakage. Same result a week later, that's how you know you got a winnah.


You could also build the circuit from this site, looks like something we should all have on our benches.

http://www.electrojumble.org/reforming.htm