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

[Carl]

A lot depends upon the quality of the cap to start with, its enviroment 
which also includes RF since electrolytics react poorly to it as seen in 
Dentron amps with only 500pf plate choke bypasses that are run hard on 
160/80M.

Many of the amps I get in for service have 80's date codes on the caps and 
those I always strongly recommend get changed. Subsequent testing confirms 
leakage is already in the twilight zone but not yet dangerous.....on most 
but there are exceptions.

Since Computer Grade caps arent that expensive its good insurance. I buy all 
mine, no matter the amp, from Ameritron at $13.50 each for 270uF or $108 for 
8 of them. These fit the Alphas, Amp Supply, Ameritron and a few others.

Other amps such as Heath, Command, QRO, etc get the CDE 381LX series 330uF 
450V 105*C caps from Mouser at $14.75 a pop but I buy the 25 qty at $9.95 
since I use so many. They are also retrofitted into amps using the twist 
lock cans and the 30mm dia 220uf fits the NCL-2000 clips perfectly.

Since the tolerance is far better than originals I cut down on extra heat 
and current by replacing 30-50K equalizers with 100K 3W MOX.

Carl
KM1H




----- 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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>
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