[Amps] How to know when filter caps begin to fail

[Carl]

After a short time reforming of modern caps anything over 1ma at 450V I 
consider junk.
Ive also rejected new caps that started acting up at around 440V which 
caused Ameritron grief when I told them. They found out their supplier was 
short changing them on the aluminum and have been testing....and rejecting 
since.

I buy large amounts of repair parts from them so they listen when I report a 
problem.

Carl
KM1H



----- Original Message ----- 
From: "Gene May" <gene-may at hotmail.com>
To: "Amplifier Mailing List" <amps at contesting.com>
Sent: Wednesday, March 28, 2012 8:19 PM
Subject: Re: [Amps] How to know when filter caps begin to fail


>
>
> 1.  I, too, have shared Bob K6UJ's experience with an electrolytic cap 
> exploding, and the mess was awful enough to make me conservative about the 
> issue of replacement.  The goo between the foil seems to be somewhat 
> corrosive, was slow to clean off, and  damaged some of the metal it got 
> on.
>
> 2.  I'm cheap, and have used many surplus electrolytic caps.  Along with 
> Glen K9STH's suggestions, I suggest that anyone also using surplus caps 
> connect them in series and place some DC across for a few hours, then see 
> how much they leak.  I toss anything that gives off any more than a few 
> watts -- I've seen leakages of 20 - 30 mA at voltages of around 300V (6 - 
> 9 watts) on surplus caps -- and know others who are even more conservative 
> than I about throwing them out.  They can be so much cheaper than new that 
> I think it is cheap insurance being conservative.  Along with Glen, I have 
> found that frequent usage tends to make electrolytic caps last longer, not 
> go bad faster.
>
> 3.  Finally, particularly if you use surplus caps, I suggest that AFTER 
> THE CAPS ARE THOROUGHLY DISCHARGED, every so often it is worthwhile to 
> simply feel them after they have been under power for a few hours, and 
> replace the whole batch if any one of them is particularly warm.
>
> Gene May
> WB8WKU
>
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