[R-390] killer and mica caps

[Larry H]

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