[Ron Ramirez]

Cardboard or fiberboard...its purpose, I think, was to help insulate the ends of the field from the "pot."

I've never heard of asbestos being used in Philco speakers.

Philco made most of their own parts until 1938. Early on, Jefferson Electric made at least some of their transformers and chokes. After a 1938 strike, Philco began to use more parts from outside sources. Scroll to the bottom of this page for more info:
http://www.philcoradio.com/history/hist3.htm