General Electric Types D-6, D-7, and D-9 polyphase

Types D-6 (1915 to 1928), D-7 (1923 to 1928),
D-9 (1925 to 1928), D-8 & D-13 (1925 to 1934?)

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With the introduction of the I-14, the D-3 and D-4 gave way to a new family of polyphase meters. As with the I-14, the terminal covers of the D-6 are captive, sliding out of the way when access is needed. The D-7 is a slight improvement over the D-6 with its removable terminal covers. The D-9 is a 3-stator version of the D-6. As with the I-14, these polyphase meters were available with either metal or glass covers.

Shortly after the 25Hz I-14 was split off to become the I-15, the 25Hz version of the D-6 became the D-8, and the 25Hz version of the D-9 became the D-13. Otherwise, these meters are identical to their 60Hz versions.

David Kingston collection