[Arran]

There is a difference in the RF section of the 37-116 and the late model 38-116 code 125 chassis. 

The 37-116 and the early 38-116 use a simple padding arrangement for the short wave bands which tends to compress the dial scale at the high end of the bands and expand it at the low end. The later 38-116 code 125 (and the 38-690) use a different RF section with split stator tuning cap gangs which provide a more linear calibration of the dial. Many of the alignment trimmers were also eliminated with this arrangement. You can tell the revised front end by looking at the RF amp tube. It uses a round aluminum tube shield and a 6U7G instead of the 6K7G with the usual square shield.

Philco must have thought it was an improvement since they used the identical revised tuning system on the high end 38-690. 

 Anything that results in a more linear tracking or stations on short wave sounds like an improvement to me.
Regards
Arran