Earlier today, "Unbeldi" posted a response to a question posed by a brand new member to the forum, regarding the wiring and operation of a Western Electric 140-AL anti sidetone (AST) desk stand. His explanation was concise, and easy to understand for someone new to the hobby of antique telephone collecting. For this reason, and with "Unbeldi's" permission, I've combined the information he posted, into a "PDF" document for future reference for everyone on the forum, and attached herewith.
Jeff Lamb