[AMRadio] looking for HRO tuning knob

[Donald Chester]

If it's an early HRO with the German silver dial (not painted black), do not 
destroy the dial.  Replacements are almost impossible to find.

Also, never use emery cloth,sandpaper or other abrasive to clean  those 
dials.  I always preferred a cloth lightly oiled with WD-40, and lots of 
polishing using a soft cloth.  Eventually the oxide will go away and some 
shine can be restored.  Abrasives will permanently ruin the surface.

I once bought one of those receivers thru the Yellow Sheets.  The receiver 
was in excellent condition, but the seller said that before shipping, the 
dial was a little corroded, so he "polished it up for me."  He had  sanded 
it with a fine grade emery cloth, and the dial calibration markings were 
partially and permanently eroded away.  Reminds me of the time when I was 
about 7 years ago, and I got into my uncle's collection of Indian Head 
pennies.  I used sandpaper to shine some of them up to a bright copper 
finish.  No need to even mention his reaction.

National replaced the dial with the black painted version after the first 
year or two of production because the German silver tends to tarnish to a 
dull finish.