[AMRadio] I hate Micamolds


Rob Atkinson ranchorobbo at gmail.com
Sun Nov 19 22:16:26 EST 2017


There's a complex byzantine method for telling micamolds from real
micas and I read it once in an email post to some boatanchor list, but
I can't remember what I had for lunch Friday, and there's no way in
the world I'll ever remember the fine points or dull points of mica
disambiguation, so they all get shotgunned out if it's up to me and I
move on.  That method saves more time than repeated crapouts.


73

Rob
K5UJ

On Sun, Nov 19, 2017 at 5:50 PM, CL in NC via AMRadio
<amradio at mailman.qth.net> wrote:
> Micamold caps have to be the best 'planned obsolescence' part ever made.  These caps that can fool you as they look like a common postage stamp mica, always need to be checked.  I have never found one that was not more resistor than capacitor. At least they are easy to spot as the proudly print their name somewhere on them.  They are really just a wax cap in the postage stamp looking package.  I am redoing a piece of gear full of Micamolds and purchased appropriate modern replacements.  Now, your standard low value 'real' postage stamp micas seldom give me a problem and I didn't even bother to spot check any of those.  Well, I discovered this unit has a bunch of .01 postage stamp style micas that I overlooked, and on the cap checker and ohm meter, they are leaking.... a bit.  Now these are all in circuits with only 28VDC on them, and they show 100+meg, and short on the cap checker at around 75 volts, they are supposed to be a 300volt cap.  These are all in bypass situations,
>  no freq determining or coupling use.  What is a consensus on changing all these out?  100+meg is plenty or 100+ meg is a leaker?  100+ meg on a screen circuit to ground fed through a 47K from B+ will not load the circuit down that much, but how effective a bypass cap will it be?  Thanks for some thoughts on this.
>
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