212-HD 130 date of manufacture

I am trying to determine the date of manufacture of a 212-HD 130.It is serial no c001983,has design and circuit patent pending written above the power light.Also it has celestion G-12 65 speakers and 12ax7 phase inverter.Regards Graazzy.

The serial doesn't always mean anything. Does the amp have silver grill badges? Does the amp have a 12AX7 tube in addition to the 4 larger output tubes?
Taking the chassis out of the cabinet and looking for test and production date codes or labels is usually the most accurate way of dating a Music Man amp, but the answeres to the questions above should help narrow it a bit.
One thing is for sure, it was made before 1980-81 as it was replaced by the 150 series in the 1980 catalog (which is posted in the Manuals area of this site).
Steve