The cover of my 1947 PRR Timetable:
When this timetable was printed the decision had already been made to convert all PRR Varnish to Diesel Electric power.
ON EDIT: This is the 1947 timetable, not 1949, which explains the T1 on the front cover. In '47 the T1 was first-line power. The decision to go Diesel for the varnish came in 1948.