High ESR capacitors

When electrolytic capacitors age, many changes can take place:

• drift in capacitance
• increase in ESR
• increase in leakage current
• open circuit
• short circuit

High ESR is a common problem. It is easy to test for this without removing the capacitor in question. Connect a good capacitor in parallel with the capacitor in question. If the problem goes away, the original capacitor is probably bad due to high ESR or reduced capacitance.

Modern electrolytic capacitors are available in a wide variety of ratings and shapes. Replacing old electrolytic capacitors with new ones is a straightforward procedure. Just make sure that the new one can fit, mechanically.

Old devices should be powered on from time to time, to keep the old electrolytic capacitors formed. If this is not done, the forming current at power up may be extremely high and the electrolytic capacitors or the rectifier tube may be damaged. Old devices should be slowly started up with a variac, over some minutes.

• Tim Reese's page on replacing electrolytic capacitors