Spent the day playing with the volume control/switch. Cracked it open, cleaned it, tested it. The arm makes contact at the outer edge of the graphite race, and the sharp resistance drop happens at the chipped area.
https://picasaweb.google.com/lh/phot...eat=directlink
Added graphite to the chipped area and retested it. Result is similar to that in the first picture except it starts at 20K ohms instead of 10K. Interesting that you asked about the part number. Much earlier I collected this information:
https://picasaweb.google.com/lh/phot...eat=directlink
I also gleaned all the part numbers I could from Montgomery Ward and Wells-Gardner in Rider's. This is a list of the volume control part numbers. I also found a note that their part numbering system was changing in the early 1930s.
https://picasaweb.google.com/lh/phot...eat=directlink
All I have to go on is that my schematic says R1 2,500 ohms.
I have a spray can of Slip Plate (dry lubricant--graphite and nickel in water) which I used to coat a CRT. I may experiment with that on strips of paper or felt to see if I can create a good resistance curve.
Thanks again. I'll put this away until tomorrow night. Have a good President's Day.