[LASJayhawk]

Is there a difference between the ones used in 37 (4 tabs or the base at the socket) and 39 (has the base that requires you to use a 'G' type tube?

[Ron Ramirez]

No difference in the shields themselves, only in the shield bases.

1937 shield bases are the best if you need to change a base out, because they only have four flat "fingers" that hold the shield, allowing you to use any type of tube that will fit the socket - G, GT or metal. But 1936, 1938 and 1939 bases have an opening where only a "G" tube will fit. (This did not apply to 1936 models as only standard base tubes were used in the 1936 Philcos, not octals.)