[Amps] How Do You Know When Filter Caps Begin to Fail?

[Paul Christensen]

Temperature and working voltage are the major drivers affecting life span. 
Roughly, for every 10-degree C reduction in rated working temperature near 
the maximum working operating voltage, life doubles.

I've been changing electrolytics when they've been in service for about 20 
years -- sooner under high operating temperatures.  I recently re-capped an 
Alpha 86 and due to the high cost of computer-grade electrolytics, the 
project cost about $175 for seven OEM caps.  Still, life of an electrolytic 
cap seems to vary wildly.  For example, filtering and regulation in several 
of my ca. 1930s National power supplies remain excellent and the caps are 
now 75 years old.  Back then, any electrolytic cap greater than about 10 uF 
(at 350V +) was a rarity and it wasn't until after WWII that manufacturing 
processes became better, allowing for greater cap density.  With older 
electrolytics, I don't go through a ramping up routine with a Variac device 
either.  If it works, great.  If it fails on power-up then it was on the 
ragged-edge of reliability anyway and in need of replacement.

Oil-filled HV caps seem to rarely fail.  No doubt it happens, but overall 
they appear to have long life spans.

Paul, W9AC

----- Original Message ----- 
From: "Bob K6UJ" <k6uj at pacbell.net>
To: "amps at contesting.com" <Amps at contesting.com>
Sent: Wednesday, March 28, 2012 4:33 PM
Subject: Re: [Amps] How Do You Know When Filter Caps Begin to Fail?


> Pete,
>
> My understanding from input received on this reflector is that the 
> electrolytic filter caps have reached the end of their lifespan and
> are prone to go out after about 15 years.  This varies of course but it is 
> good idea to change them out if they are as old as yours.
> The problem with these guys is that when they go you don't normally have 
> any pre indication and they usually go kaboom and take out
> other stuff along with it.  Cheap insurance to replace them.
>
> Bob
> K6UJ
>
>
>
> On Mar 28, 2012, at 9:16 AM, Pete Smith N4ZR wrote:
>
>> I have an SB-220 that dates at least to 1978.  There is no external sign
>> of any problems, and the amp has been heavily used in contests for at
>> least 20 years.  It still delivers over 1300 watts on 80-20.  Is there
>> going to be any warning of a capacitor failure?  Will there likely be
>> any cascading damage to other components? Is it conventional wisdom that
>> I should replace them as a precaution?
>>
>> -- 
>> 73, Pete N4ZR
>> The World Contest Station Database, updated daily at 
>> www.conteststations.com
>> The Reverse Beacon Network at http://reversebeacon.net, blog at 
>> reversebeacon.blogspot.com,
>> spots at telnet.reversebeacon.net, port 7000 and
>> arcluster.reversebeacon.net, port 7000
>>
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