[Boatanchors] [BoatAnchors] [Milsurplus] Micamold Recovery

[K5MYJ]

I have a National NC-109 that has 8 of these red square capacitors with 
three rows of dots in the LO.

A few years ago I tried to calibrate the main tuning dial. I was able to get 
the all the bands except the "C" band to calibrate correctly. I could not 
get the linearity correct on the "C" band. The "C" band has 40M on it.

I was told it was most likely one of these capacitors.

This radio has a LO assembly that can be removed from the chassis but it 
requires cutting 8 leads from the band switch.

I have been planning on removing this assembly and replacing the red 
capacitors with CD DM-15 silver mica capacitors. While I am at it I am 
considering replacing every capacitor in this receiver.

And every out of tolerance resistor.

That probably means a complete rebuild!

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "L L bahr " <pulsarxp at embarqmail.com>
To: "David Stinson" <arc5 at ix.netcom.com>
Cc: <boatanchors at mailman.qth.net>; <milsurplus at mailman.qth.net>
Sent: Wednesday, June 04, 2014 9:45 PM
Subject: Re: [Boatanchors] [BoatAnchors] [Milsurplus] Micamold Recovery


> Hey Dave,
>
> Good luck with your venture.  I'm one of the guys who frowns on using 
> them.  However, tat said, your logic is sound.  Just different strokes for 
> different folks.  I am usually a stickler for keeping things stock and 
> original, but when it comes to caps, I go for the new ones.  You can't see 
> them once the radio is back in the case, they are electrically superior 
> and very cheap to buy these days.  A couple years ago I refurbished a 
> Johnson Viking I and I think it had 21 of them in there as I recall. 
> Everyone of them was bad and actually was producing a voltage as if it 
> were a battery.  I replaced all of them with disc ceramics, but that story 
> in itself would bring on many positive and negative comments from some. 
> Anyway, just wanted to let you know even though I would not use them, your 
> topic was interesting and you have the right to try things that interest 
> you and do things your way. The most important thing is too have fun doing 
> what you are doing in ham radio.
> Lee, w0vt
>
> ----- Original Message -----
> From: "David Stinson via BoatAnchors" <boatanchors at theporch.com>
> To: boatanchors at mailman.qth.net, milsurplus at mailman.qth.net
> Sent: Wednesday, June 4, 2014 2:00:28 PM
> Subject: Re: [BoatAnchors] [Milsurplus] Micamold Recovery
>
> Thank you for all the input.  I do understand the
> "conventional wisdom" concerning MicaMolds,
> but I'm not convinced just yet.
> Here's why:  These caps were all produced about
> 70 years ago and have been taking-up water at about
> the same rate.  They have been aging as a group.
> Capacitors or coconuts- age a group of things
> produced at about the same time and they'll
> all be in about the same shape.
>
> We got them over the last 20 of those years.
> Many of them have taken-up water (as would be
> expected) and test "bad."
> We've had to change them, leading us to curse them
> and just change them all- it's only human nature.
> But, as far as I know, no one has tried to drive the
> water out, re-seal them and see if they can make another
> 50 years (or better, since we have better stuff to seal them).
>
> I like the way they look and I like the possibility of
> "original replacements."  Got nothing to lose but a little
> time and effort.   So here's what I plan to do:
> Coat the "dried-out" caps with varnish or poly..
> anyone know which is a better water barrier?
> Then build a low-freq oscillator using all of this
> handful of caps, plug it in and leave it running
> for a loooooong time.  Like two years.
> See what the "mean time between failures"
> really is.  If they stay in service with no failures
> for a year or two (which passes quickly at our age)
> or if they pop like popcorn after a week,
> I'll let ya know.
>
> 73 DE Dave AB5S
>
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