Why you should replace Capacitors.

[Penthode]

Originally Posted by DavGoodlin

By dielectric reforming, are you referring to a re-establishment of the rated capacitiance in a "partially open" electrolytic?

I was originally thinking this meant to restore the integrity of the dielectric if it was leaky.

I was actually referring to the leakage problem. If the capacitor has been sitting for many years unused, then the dielectric leakage will increase. Plugging in a set which has been unused for decades is asking for trouble.

I use a Sprague TO6 Capacitor Checker to reform the dielectric. The TO6 has a hi voltage power supply with a milliammeter. I will find that if I apply a voltage across the capacitor and limit the initial leakage to no more than 6 mA, over time, the leakage will drop. I will reach full rated voltage within an hour or two and the leakage will drop below 100 microamps. If the leakage remains low, then the capacitor should be okay so long as the capacitance measurement is correct.

After this process, I have had a capacitor open circuit but never short. I have had a set where someone plugged in the set before I have had a chance to reform the capacitors. In this case I have found capacitors only rarely irrepairable. The old Sprague and Mallory aluminum can capacitors have great healing ability.

I am amused by others who immediately replace the electrolytics without first checking them. I wonder whether the replacement being stuffed into the old cans will last as long as the originals!