[Tim]

The following notes regarding 48-1000 chassis codes are from Radiomuseum.org:

Three chassis codes were used in the following chronological order: code 121, code 125, and code 122. Codes 121 and 125 are similar, both having 26 tubes. In code 122, the 1N34 crystal diode DC restorer was replaced with a 6AT6 tube, bringing the tube count to 27.

Philco had other TV models with similar chassis. Model 48-1050 was a console version of the 48-1000, with the same three available chassis codes. Model 48-1001 is another table model electrically identical to 48-1000 code 122, but has a simpler cabinet style. Models 48-1000-5, 48-1050-5, and 48-1001-5 have power supplies designed for 50 Hz AC supply, but are otherwise identical to the models without the -5 suffix. Model 48-2500 is a large console projection set with a chassis based on the 48-1000 design, but with several significant changes to support the projection CRT system.

Information from Riders 2 production changes says that the last 2 digits are the run number. The stamped numbers on my set do not follow this format however. Mine follows the convention mentioned in Riders 1 for code 121 units where the run number is a single digit and there is no leading 0 at the start of the stamped numbers. This is the second image below. I speculate that the series of numbers between the "11" and the run number is the serial number. This puts my chassis at 777 which is in the first 1000 which jives with the medallion on the cabinet.