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National NC183D-How To Remove Phasing Knob




 
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Author Topic: National NC183D-How To Remove Phasing Knob  (Read 401 times)
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W3ON
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« on: August 14, 2019, 03:28:33 PM »

GA All.
I have been doing some cleaning of my National NC183D receiver. Notably cleaning knobs.
The dial skirts on my NC183D were very dull and dirty. I did quite a bit of research on the internet, but found mostly very poor suggestions. Some said try and get replacements (almost unobtainable), rather than try to clean them. So, I decided to clean them. I removed each one of them, one at a time and cleaned them with:
1) Cotton Swabs and shop rags.
2) Dish Soap and Water-It did get rid of some of the dirt, but each knob generally were still messy at best.
3) Tried Isopropol Alcohol 91%. That helped but I noticed that rubbing resulted in some sort of bronze color showing through the dial skirt. Hmm.
4) Tried Novus #3 and #2 Scratch Removed. That worked better than Isopropyl Alcohol. Result was that more Bronze color was showing through .
5) Tried Mothers Mag & Aluminum Polish. That did a much better job, although that Bronze color was showing through.
Finally after doing quite a bit of studly, I found that the Bronze Color on the Dial Skirt was the color of Anodized Aluminum, which can be Bronze colored-depending on how the knob was dyed during manufacture.Hmm. I really liked that color. So, I took my time and cleaned all of the knobs with dial skirts to where the Anodized Aluminum (Bronze) color showed. Yes, I know its not the actual Dull Aluminum Color of the NC183D knobs. But I did not care. I like the Bronze color of the dial skirts.

Now I only had one troublesome knob. That was the Phasing Control knobs. That blasted thing would not come off of its shaft. Again, I rear and read on the internet for advice. Some folks gave me information that proved to be correct. Here is what I found on my NC183D. The Selectivity Phasing Adjust Control Knob is attached to a Shaft Coupler with a round piece of 1 inch long by 1/4 inch diameter phenolic material. This long shaft extends the range of the Selectivity Phasing Control, so that the Selectivity Phasing Control Knob can be attached. I could not get that knob off the shaft. So, after much experimenting I found that I had to remove the cabinet from the chassis, by removing all screws on the back, bottom, and sides. Then I had to work the knob by pulling on the front panel until all of a sudden it popped off. That was the only thing that worked for me. Some had suggested removing the shaft extender coupler. That did not work for me as they was literally no room to get a hex wrench on the shaft coupler hex screws.

So, at the moment I am just about done with the knobs.

Well, I hope this might help you, if you are trying to do this.

If I can figure it out I will see if I can post some photos.

73 de Chuck W3ON


* NC183DKNOBPHASE-1 copy.jpg (260.1 KB, 2848x2134 - viewed 59 times.)

* NC183DKNOB-8.JPG (1164.58 KB, 2848x2134 - viewed 49 times.)
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MikeKE0ZUinkcmo
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« Reply #1 on: August 14, 2019, 05:57:23 PM »

You might consider removing the coupling, chucking the shaft into a  drill motor and using some sand paper to reduce the shaft's diameter a few thousandths, so next time you won't have that problem. 

Interestingly, I've had 3 183s over the years and never had that particular problem.

Before you go any further, I would make sure to note the positions of the set screws for both the knob and coupling, by looking at the markings on the shaft, and placing  dots at the edge of the ends of the shaft, so when you re-assemble things, you can get the knob oriented as it was originally, since the positioning of the skirt markings is important in interpreting the operation of the crystal filter.

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Mike KE0ZU

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W3ON
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« Reply #2 on: August 24, 2019, 01:27:11 PM »

GA Mike
Thanks for the tip. I did indeed remove the phenolic extension and lightly sand it so that it fits properly. It no longer sticks in the coupler.
Lately I haven't been doing much on t he NC183D. I did manage to clean the exterior of the chassis, using a combination of Mothers Mag/Aluminum cleaner and light sand paper.
In the process I erased the lettering at the rear of the chassis. After doing some searching for dry transfer lettering (unobtainable), I ended up creating some labels using a Brother PT-80 Label Maker, with M131 (Clear with Black printed labels). I have them installed. Plus I used some 'Interior/Exterior Gloss Varnish' that I bought at a Hobby Lobby store as a sort of clear coat. Now I am again looking at the top of the chassis. I had cleaned it awhile ago, but don't like it. I may redo it again now that I have the chassis out of the cabinet.
I also found that a previous owner has removed the 5U4 tube and replaced it with a solid state replacement.
Of course there is no documentation. There is a potentiometer mounted at the rear of the chassis. Tracing the wiring
it appears to go to the 5U4 tube socket. I am assuming that it is used to set the B+ voltage.  It is marked as a Millen/Malden 74400-4 whatever that is. So far, I have not found any information yet.
Oh well.
73 de Chuck W3ON
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kb2vxa
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I modulate, therefore AM


« Reply #3 on: September 10, 2019, 11:55:46 AM »

Hi Chuck,

Better late than never, I have the answer to your problem. First. why document changing a vacuum rectifier with a solid state one? If it was an under chassis addition of a couple of diodes I can see documenting a wiring change, but replacing plug in units so obvious I see no need.

Here's what you DO need, a photo of the rear chassis skirt so you know what's there and replace the lettering. If all else fails a Sharpie may be crude and requires a steady hand bit it works. That mystery pot in the center is the S meter zero adjust, it looks like you didn't trace the wire far enough. The meter is in the center of a sort of Wheatstone Bridge circuit, changing cathode current in an IF tube through a resistor in the bridge changes the meter reading. That pot is in the other leg of the bridge, when no signal is present and IF current at idle it balances the bridge and results in a zero reading. With that in mind the terminal on the 5Y3 socket (a 5U4 is overkill and draws more filament current, 3A vs. 2A) is unused by the rectifier and used as a tie point by National.



* NC-183D x back.JPG (269.84 KB, 800x533 - viewed 28 times.)
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73 de Warren KB2VXA
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kb2vxa
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I modulate, therefore AM


« Reply #4 on: September 10, 2019, 11:58:07 AM »

The pdf schematic didn't "take" the first time, try try again.

* nc-183d_scematic.pdf (4635.53 KB - downloaded 12 times.)
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73 de Warren KB2VXA
Station powered by atomic energy, operator powered by natural gas.
MikeKE0ZUinkcmo
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« Reply #5 on: September 10, 2019, 05:51:51 PM »

Looks like the rear apron Warren shows has a few extra connectors on it.

Here is a pic of the rear apron on my 183D.


---------------
Are you saying there are two pots on the rear apron?

 
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Mike KE0ZU

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kb2vxa
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I modulate, therefore AM


« Reply #6 on: September 13, 2019, 07:43:37 AM »

The S meter zero is in the usual place where most are found, I don't know of any more. I got the photo and schematic off the Internet, there's no accounting for accuracy especially with photos. What those SO-239s are for I have no idea, I never owned the unit, the whole idea was showing the pot. That unit may have been modified, there's more "junk in the trunk" than any National I've seen personally. I can say however that the schematic is for the D model.
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73 de Warren KB2VXA
Station powered by atomic energy, operator powered by natural gas.
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