The primary stations of the "WJZ chain" were RCA's WJZ (now WABC) in New York City and WRC in Washington, DC, plus General Electric's WGY in Schenectady, New York and Westinghouse's WBZ near Boston, Massachusetts.
Map of the "WJZ Chain" radio network, from Radio Broadcast, "How Much It Costs to Broadcast", by Austin C. Lescarboura, September, 1926, page 370:
1926 WJZ Chain
Programs which originate from the WJZ studio are frequently distributed to other stations indicated on the map. Repeater, or stepping up, stations are indicated where the program, forwarded by wire, is increased in volume by amplifiers. In addition to WGY and WRC, WCAD, WBZ, KDKA, and KYW are sometimes included in this group