Western Electric 400D - Modification for Bridged Ringing

This is a snapshot of Doug Alderdice's 2014 document on how to modify Western Electric 400D line cards (pre-issue 15) for bridged ringing, as these older cards only ring with grounded ringing unless modified.

Doug found a way to make the modification as simply as possible, adding a single resistor and cutting a trace; amazing work on his part! See the text for a full description.

For whatever reason I always find it hard to locate his document through google whenever I need to show it to someone, so snapshotting it here.

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