03-18-2014, 01:06 PM
I think you might be talking about the Automatic tuning dial with "Magnetic Tuning." Here is an article from Chuck Schwark's web site that should answer most of your questions.
http://www.philcorepairbench.com/autodial/index.htm
http://www.philcorepairbench.com/autodial/index.htm
John Honeycutt