[JMS] National PW Dial Patent?

[JAMES HANLON]

Y'all,
 
For an article that I'm writing for Electric Radio Magazine, I'm trying to find out if there was ever a patent on the National PW dial used on the HRO receiver.  On the James Millen Society web site at
http://www.isquare.com/millen/bio_rem/merrill.html
there is an article with a picture that includes “original letters to and
from Millen and Clarence D. Tuska relating to the patent on the famous National
PW dial drive assembly, often refered to as the HRO dial.”  The person who assembled the items in the picture is Merrill W. Bancroft.  It was his display at the 2001 AWA Conference in Rochester, NY.  



I'd appreciate any information on the subject that anyone might be able to supply, including any leads to Mr. Bancroft if he is still with us and any ideas about the patent on the PW Dial drive.  
 
Thanks very much,
 
Jim Hanlon, W8KGI