Sunday, November 6, 2016

Something Different - National NC-109

 I need another old SW receiver like I need another hole in my head, but I felt sorry for this old NC-109 when it came up at an auction I attended last summer and nobody wanted to bid on it.  I don't remember what I ended up giving for it, but it wasn't much.

Other than being dirty, it appears to be all there, so let's see what we have:

 Typical dusty, dirty chassis - looks like a layer of nicotine residue, but no rust or mouse damage, and all the tubes are there.  We're off to a good start!

This is interesting.  At the top of the chassis, it looks like someone hacked-in a 40uF electrolytic and 500 ohm wirewound, probably because the multi-section filter cap wasn't doing it's job. Sigh. Kids.  

That was an easy fix, though, and what's cool is that there aren't many tubular paper caps to deal with - National used ceramics for bypassing, and those don't usually fail.

Normally, I like to remove and restuff chassis-mounted electrolytics, but I really don't feel like this rig is worth the effort.  I might change my mind tomorrow, but for now, I've disconnected the can and installed new caps on a terminal strip.

Now for the fun part!  After changing the filters and inspecting for any other obvious problems - time to power it up!  I don't have any pics of this process (not much to see, really) - I use a variac connected to an isolation transformer, and bring it up slowly, watching for any signs of trouble.  This old National fired right up - no magic smoke was released!  Yippee!

At this point, I gave it a quick evaluation, starting a "punch list" of things still needing attention:
  1. Band 1 (AM BC) is dead.
  2. Strange AVC "pumping" and background noise - mixer?
  3. Dirty controls/switches.
  4. Main tuning and Bandspread caps stiff - need clean/lube.
  5. Rudimentary cosmetics / degrunge.
  6. Screw terminals for antenna disconnected/rerouted to added SO-239 - need to be restored (why do people do this?)
Nothing looks too bad.  On the good side: 
  • It receives: Envelope and product detectors are both working.
  • ANL works.
  • BFO works.
  • Crystal filter/selectivity switch works.
  • Dial calibration is reasonably close.
  • Only a handful of tubular paper caps and one LV electrolytic (AF cathode bypass) to replace.
  • Nothings smoking!
So, barring anything unforeseen, should be able to whack this one out in a few nights.  Wish me luck!!!

73 - Steve


  1. I'll watch this one with interest , Steve. I have two of them sitting under my desk waiting for me to get to them. Currentlly working on nasty RCA 811K, Scott AW 15, & a Zenith TV. May succeed with at least one .. not good at it.
    Keep the nice posts coming on Facebook!
    Ken, KE1RI,

    1. Thanks, Ken!

      Good luck on the projects. It sometimes takes a lot of patience and tenacity to get these things done. Fortunately, there's no deadlines to worry about :-)

      I've got 3 old TVs and I think that'll be it; they're just too time consuming. My grandson is nuts over the CTC-19 in my "shack" - I think it's because he's never seen a TV with knobs before (he's always twisting them to see what happens - future Radio/TV nut?)