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