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clm811 22nd February 2010 09:56 PM

Life expectancy for used electrolytic caps
I'm upgrading a Forte power amp and recently bought some large surplus electrolytic caps. These replacements are 47,000uf, where the originals were 15-18,000uf.

I understand the date code indicates they were made around 7 years ago (these were purchased "new" in the box from surplus).

I've read where it was recommended "ANY electrolytic more than about 12-15years old should be replaced."

As these were stored for approx 7 years, does it mean they won't last more than 5-8 years once in use (or should I expect 12-15 years of actual use)?

Also, since these have never been used, I've been advised to "form" them using a series resistor(20-30kohm) and variac to gently bring up the DC voltage to the needed level(then discharge them gently through the resistor).

Any advice/experiences regarding this are appreciated.


Xoc1 22nd February 2010 10:24 PM

I would not hesitate in trying out these capacitors they should be fine, especially if you 'reform' them. Most quality electrolylic resevior capacitors should survive up to 20 years on the shelf - Capacitor life is severely shortened when they reach high temperature in use.
Are you sure that the rest of the amplifier is up to the increase in inrush current at switch on:eek:

Steve Dunlap 22nd February 2010 10:36 PM

1 Attachment(s)
I feel the general attitude about electrolytic capacitors is incorrect. The shelf life can be 16 years or more. This can be extended by reforming or applying voltage, as in use. You may find the attached paper of interest.

sumaudioguy 23rd February 2010 04:24 AM

Caps mostly get old in use and/or with elevated temperatures. Sitting around they age and very slowly deteriorate. 25 years and most still seem to work. Thing is these new low ESR high speed caps are so much better than anything from even 5 years ago in these big value available now. Just switched to 100,000F switching caps for rebuilds. Yes they are better in about every way and yes they test and sound better also.

pforeman 23rd February 2010 04:55 AM

Not quite sure if I got this part right.
Applying voltage reforms caps.
So regular use will regularly reform your caps.

wow what a long paper

clm811 23rd February 2010 07:13 AM

1 Attachment(s)

Are you sure that the rest of the amplifier is up to the increase in inrush current at switch on{?}
Well, the power transformer is HUGE, and the 2 bridge rectifiers look like at least 20A units (photo of similar amp is attached). It appears that there is a current-limiter (thermistor?) before the power transformer, so I hope its safe to triple the PS caps.

I'm thinking about replacing the bridges with some of the way-cool HexFRED units- should I go for the 27A or the 32A rated units?

Any experienced advice here is appreciated.


h_a 23rd February 2010 07:39 AM

Generally, the bigger the better.

A blown bridge is complete desaster ;)

Have fun, Hannes

PS: continous current rating has not much to do with inrush current. High inrush needs high peak current rating, typically above 100A or so.

east electronics 23rd February 2010 03:36 PM

a lot have to do regarding endurance the way and the quality of built

in the times of vintage service were most of electrolytics of most of our costumers getting replaced anyway then the "broken" parts some times we test with various methods and surprize surprize still work like hell

some companies did an excellent job regarding power supply capswhile some others did horible choices for their machines

i have sen models of nakamichi working for 25 yeras and almnost all caps are with in tollerance and seen models of the same company that worked for 15 years and all caps inside was cr**p

repeatative presence of the specific equipment with the same problem again and again shows that the caps was the wrong choise in the first place ... presumably the company didnt know about it

sumaudioguy 23rd February 2010 04:20 PM

This is great information so thanks. Real life testing is is seriously short supply!

I strongly suspect capacitor ripple current and temperature greatly affect any caps life.

Conrad Hoffman 23rd February 2010 04:31 PM

I have literally thousands of capacitors, mostly surplus, from nearly new to as old as dirt. The only ones that show any signs of deterioration are the HV twist locs up at 450 volts or so. Anything else can be pulled from its box, bin or bag and used without forming or anything else. The HV caps need to be slowly formed if any reliability is to be had. Newer brand name caps are better, not because they're newer, but because they're just made better from day one. Technology has advanced. Newer off-brands should be approached with caution. As I've said many times before, the best practice is to build (or buy) a simple bridge and measure the things. If C and D are good, and leakage is low at full voltage, you've got nothing to worry about.


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