[Boatanchors] NC-109 Help Needed

[John Marshall]

Joe,

The individual page schematic on the BAMA mirror is a lot clearer than 
the PDF version.  I have no trouble making it out on my 'puter.  It's 
on two pages:
http://bama.edebris.com/download/national/nc109/12.gif
http://bama.edebris.com/download/national/nc109/13.gif .

The NC-109 didn't have any provision for external muting so you don't 
need any jumpers in the accessory socket unless the set was modified.  
According to the schematic, pins 1, 2 and 3 on the accessory socket 
should be unused, so if you see connections there it might indicate a 
mod.

Assuming you tried swapping out the 12AT7 and 6AQ5.  I don't recall 
exact values from my 109 but look for full B plus (200V or whatever 
your PS puts out) on the 6AQ5 plate (pin 5) and 180V or so on the 
screen (pin 6).  The cathode (pin 2) should probably be around 10V give 
or take.  No voltage on the screen would indicate a problem with the 
Receive/Standby switch.  If those voltages are good, you might be able 
to hear a click by probing the 6AQ5 grid (pin 1).  The Tone switch 
shunts a capacitor from grid to ground so check to make sure it or the 
capacitor is not shorted.  The 12AT7 first audio will have a pretty low 
plate voltage but it also comes thru the Standby switch.

GL troubleshooting!  This makes a nice receiver for SWLing and the 
sharp crystal filter makes it pretty good for CW on the low bands.  I 
used mine on 80 last year for SKN and had a great time.

John, KU4AF
Pittsboro, NC


On Tue, 26 Sep 2006 22:53:37 -0400, Carole White-Connor 
<carolew at bellatlantic.net> wrote:

> Hello, all. I just picked up a National NC-109. It was sold to me as a
> basket case but it actually does not look too bad. It should be a fun
> project.
>
> 1.  Does anyone have a voltage chart? The manual I downloaded from 
> BAMA does
> not have one.
>
> 2.  Does anyone have a legible schematic. The BAMA one is tough to 
> read.
> Surprisingly, Sams does not list a service packet for this set.
>
> 3. My problem appears to be in the audio section. The voltages coming 
> out of
> the power supply are good. However, there is no audio and no response 
> when I
> stick a soldering iron on the volume control. The output transformer 
> tests
> good.  Does anyone know what the voltages should be on the audio output
> (6AQ5) and the AF amp (12AT7)?
>
> As always, thank you in advance.
>
> Joe Connor