[Ron Ramirez]

The change was made in December 1935, about the middle of the 1936 selling season.

All 116, 660 and 680 models had the shadow masks (giving the appearance of moving arrows) from when they were first introduced in May 1935 on throughout the 1936 season. (The 660 was replaced by the 665 in December 1935-January 1936.)

Philco called this the "Glowing Arrow Wave Band Indicator."

In December 1935/January 1936, shadow masks were added to many of the other models in the Philco line, including the following models (using the Philco Changes in Models sheets as a reference):

655 (successor to the 650)
651
645 (successor to the 640)
643
642
635 (successor to the 630)
625 (successor to the 620)
611
And, apparently, the 610 even though this change was not mentioned in the Philco Changes in Models sheets.

Addendum: Models 620, 630, 640 and 650 never had the "glowing arrow wave band indicator." If you have one of these cabinets and the chassis has the shadow mask, then it is one of the later chassis (625, 635, 645 or 655).

I think that's enough confusion for one post