"Seven Hundred and fifty stethoscopes connected by radio, enabled as many physicians to study the heart beats of one patient in the lecture hall on the Municipal Pier, Chicago at the recent convention of the American Medical Society."The calls are not mentioned but its location was. They broadcast from Municipal Pier in Chicago. Chicago only had eleven radio stations at the time and several operated share-time: 560 KYW-AM, 810 WEBH-AM, 833 WDAP-AM, 670 WMAQ-AM, 670 WQJ-AM, 870 WLS-AM, 1050 WAAF-AM, 1120 WTL-AM, 1120 WJAZ-AM, 1160 WDBY-AM, and 1210 WCBZ-AM. That's it. But the article does not describe a city-wide broadcast. It was a private affair for the benefit of the AMA. that indicates it was probably at low power and certainly indoors.
Municipal Pier was constructed in 1914. More here.The pier was renamed Navy Pier in 1927 to honor the Navy veterans of World War I. It was designed by Charles Sumner Frost. The huge pier is 3,000 feet long and 292 feet wide. But this pier was so massive it had buildings on it.After reading about them individually I am certain that it was held at "the Hall." I read a description here.
That building opened in 1916, not only making this possible but much more likely. Where else would you put 750 physicians and their stethoscopes? reading further, they also note that they used "three element vacuum tubes." Those would certainly be a triode, an early tube based on the Audion. There were severla brands at the time: Crysleco, Marconi-Osram, Ediswan, Wecovalve, Triotron etc. There's vircutlaly no way to know what they actually used. It's highly likely that some Chicago radio station had somthgin to do with the engineering but that is omitted from the story."Located at the east end of the Pier, the third section housed a half-domed shell, 150 feet by 138 feet with a domed ceiling 100 feet high. Known as the Hall, architects used radial steel trusses shaped in half arches to provide a wide, open area for civic functions or entertaining. Windows located in a 180-degree half-circle enabled a spectacular view of Lake Michigan."