[R-390] killer and mica caps

[Lester Veenstra]

The filter is the fuze

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
lester at veenstras.com
-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Renee K6FSB
Sent: Monday, October 10, 2016 10:41 PM
To: Francesco Ledda
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] killer and mica caps

I am beginning to think that a fuse in series with the cap on the filter 
side might be the answer . just a thought .......
Renée, K6FSB

Francesco Ledda wrote:
> Given the small bandwidth of the IF, the frequency/gain variation created
by the cap is negligible.
>
> Frank
> K5URG 
>
> Sent from my iPad
>
>   
>> On Oct 10, 2016, at 20:13, Larry H <dinlarh at att.net> wrote:
>>
>> Hi Chris,  I understand all of our desires to get this right, as i've had
to replace bad filters, and it's no fun or cheap, and sometimes a crap shoot
(is my replacement good).
>>
>> Here's some things to consider:
>>
>> 1. Any coupling capacitor introduces distortion into the signal path.
How much is acceptable is the question.
>>
>> 2. Adding another cap in series doubles the distortion, and doubles the
required capacitance for each one.
>>
>> 3. If I use 2 caps in series, how often will I need to test both to
maintain the desired level of safety?  Monthly? Weekly? Daily?
>>
>> 4. All capacitors fail eventually.  What is the desired and acceptable
life for C553 and can I obtain that quality of cap?
>>
>> 5. Once a self healing event occurs in a metalized film cap, can it be
determined that one did occur? No, and once they start, they reoccur at a
quicker frequency.
>>
>> 6. The life expectancy of the best quality film and foil is much higher
than a metalized film given they are rated at the same voltage and
temperature.
>>
>> 7. Should I test the replacement cap under its rated voltage?  YES!  This
is the safest way to be sure it will last.  If a new cap is bad, it will
show up here.
>>
>> I personally believe that a 630 v SBE 715P (or related) orange drop is
the best and 2 in series would not improve the safety factor very much at
all and not enough to require weekly checking or endure the increased
distortion.
>>
>> Regards, Larry
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