Elytic Cap Shelf Life

[trem]

I inherited a Kenwood stereo amp 7 years ago..
It came with a nice set of schems and a bunch of caps and some transistors for replacement.
Would you guys install a bunch of electrolytic caps that had been sitting for 7 years.?
Thank You

[The Dude]

I'd check them first. In fact, I'd check the caps in the amp first to see if they need replacing.

[Helmholtz]

Main problem with long (>2years) storage of ecaps is electrical leakage.
As leakage doesn't show with capacitance and ESR measurements, it's advisable to use a (low wattage) bulb limiter when first turning on equipment with ecaps of unknown condition.
A few hours on the bulb limiter can re-form the caps and cure the leakage if the caps are not too bad already.

[trem]

Have no idea what a modern day amp looks like.
But 1970s era integrated amps have A Lot of E-Caps in them.

I am just going to order new ones. I do not need any more worries than i already have.

Thanks Again

[Chuck H]

I remember when I still had a brick and mortar store that sold E-caps. The Sprague Atom caps at that time actually had expiration dates on the packaging. Helmholtz is correct that reforming some shelf aged caps is "plausable" but not a guarantee. I think your plan with new caps is the best idea. And even then you should still bring them up slow and then test them. Why do I say this?..

Even when I could buy Sprauge Atoms off the shelf (the only ones with a package date) I noticed that stock wasn't always monitored or rotated. Since those days I've also bought E-caps from Mouser that were shelf aged and unsuitable as sent. So I try to stick with brands and models that have the highest degree of popular opinion and usage and then order fresh for each project.

I gave up on Atom caps years ago. That doesn't mean they're bad NOW. But there were some issues with backstock being sold as new even though they were all dried up from shelf age and even couterfeit Atom caps being sold through major vendors at the time. Even practicing some care I had a couple of projects go wrong and gave up on the Atom caps forever. And now I always take readings for new caps for each project.

[Tom Phillips]

I usually slowly bring new e caps up to rated voltage while monitoring the leakage. Most do fine but every so often I find a bad one that I reject. I do this while I'm working on other projects or just other tasks on the amp that will receive the new E caps. That way I'm not really adding much time spent on the project.

I couple of years ago I found a really good price on name brand e caps from Newark. When they arrived I found that the date code was 10 years old. I don't know how to avoid such events as a small order customer.

[tedmich]

Supposedly (in the past) cap suppliers would rotate stocks and "reform" the caps periodically until some expiration date (or sale!) happened.

This was done simply by bulk heating and not any labor intensive voltage treatment Or maybe I dreamed it...

Oxygen depleted warehouses now regularly allow off season apples to be sold in the winter but like with most things, fresh is better!

[Mick Bailey]

Low voltage electrolytics don't suffer the same degree of leakage nor consequences that are seen in tube amps. The main consideration for me would be leakage in the main filter caps, but those should be easy to reform on the bench before fitting using a low voltage supply and series resistor. Even a 9v battery will suffice.

Using a bulb limiter on a SS amp has a caveat in that some amps swing and latch to one power rail if run on a bulb limiter. This gives the impression that the output stage is faulty, putting 10s of volts on the speaker output.

A variac is better in that the voltage can be bought up just enough to place a few volts on the caps and bring the voltage up gradually.