NO, no, no!The original 3 stations in the post have not 2, but 3 separate sites?
The old WPEN 950 in Philly doesn't use a critical-hours pattern, per ai4i's topic, but it has one tower site for day and a different one for nighttime.
The calls are now WKDN.
It appears that the nighttime array is located where the original 24/7 towers broadcast. The new DAYtime array is about 18 miles northwest of Center City.
OK. So far, the list (from the previous posts) looks like this:
630 KSLR San Antonio, TX
680 WCBM Baltimore, MD*
690 WOKV Jacksonville, FL
820 WCPT Willow Springs, IL
940 WMIX Mt. Vernon, IL
950 WNTD, Chicago, IL
950 WKDN Philladelphia, PA
1160 WYLL Chicago, IL
1190 KFXR Dallas, TX
1210 WILY Centralia, IL
1330 WEBY Milton, FL
1370 WQLL Pikesville, MD
1380 KXFN St Louis, MO
1500 KSTP St. Paul, MN
* WCBM does not show multiple transmitter locations in Radio-Locator. Everything else checks out.
You can use this list for more additions.
I do not know if things have changed over the years, but when WAPE (now WOKV) launched night service, they sent audio from a modulation monitor at the nighttime site back to the studio at the daytime site so the "jocks" would not go crazy listening to all the QRM on 690....it now makes for a miserable low powered night signal from the day site.