[R-390] killer and mica caps

[Francesco Ledda]

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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