In the early 1960s, the AP wire service to the radio station in my home town in Georgia was a DC pair from the telco office out to the station. I don't know the equipment used by the telco to get the signal to the home town telco central office.
Somewhere along the line, late 1960s, I'd guess, the AP converted over to the Lenkurt 25 tonepack system.
I seem to recall that the Lenkurt could handle about 25 slow speed wire circuits, 66WPM and maybe one or two 100WPM circuits. The individual printers had the single channel Lenkurt box under the M15 printer. Each of these boxes had the channel filters for the service the subscriber was paying for, but since it was an audio grade circuit, all of the channels were there on the audio pair.
The Lenkurt unit at the AP offoce was a rank mount system with all the tone modulators for the service.
As an example, the AP office in Raleigh supplied both North Carolina and South Carolina subscribers. I think there were separate state radio wires. Also on the Lenkurt was the morning slow speed newspaper circuit and the evening slow speed newspaper circuit. The stock market circuit was so large that in order to get all the data to the newspapers via the slow speed circuit, it was actually split in two, with half the markets on one circuit, the other half on a second circuit.
I just don't remember what else was on the Raleigh AP datasytem - I know it had to have more channels in use.
The AP did not have many Extel printers in North Carolina and I don't remember if any of the Extels used the external Lenkurt box or used an internal tone module.
The UPI Extel at one station I worked at in North Carolina, the tone unit was built into the Extel.