Unusually long-lived electrolytic capacitor

[MRMILSTAR]

I have a project that I built in 1969 that still operates normally. It is a small vacuum tube tesla coil (VTTC) but that is not important. One of the components is a 10 uF electrolytic capacitor rated for 450 volts which sees a maximum voltage of 350 volts. The capacitor is used to smooth the output of a full wave bridge rectifier for driving the plate of a 6L6 tube. The VTTC is used very infrequently.

My question concerns the lifetime of this capacitor. This capacitor is still functioning after 50 years! I measured its capacitance and it is within tolerance. From my reading I was under the impression that this capacitor should have dried out and died many years ago. Is it unusual to have an electrolytic capacitor last this long? Should I replace it or should I follow the "if it ain't broke don't fix it" rule?

[T3sl4co1l]

Capacitors age much more in use than in storage.  As long as it's reformed, it's fine.

Tim

[ritaismyconscience]

Did you measure the ESR? Bad capacitors may look good to a multimeter but it might have too high internal resistance to be usable.

[John123]

I'd be tempted to leave it in and see how it goes, it'll soon let you know if its on its way out!

For ESR measurements you can get those cheap all purpose testers these days for about £10, once calibrated they're right on the money.

[Hydron]

I've just recommissioned a 60's vintage Heathkit IP-20 PSU, complete with mostly or all original electrolytics (had to open it up because the power indicator bulb had come loose and it's actually part of the regulator circuit).

No obvious issues with any of the electrolytics, which is very handy as I'm in lockdown away from my normal kit and most of my spare parts, and am using it out of necessity for paying work!