The early PET models (all 2001, early 30xx) with discrete video circuitry used 60 Hz in all models worldwide.
The later PET models (later 30xx, 40xx/80xx/8x96/9000) used a 6545 CRTC chip where the ROM could set the refresh rate. (These can usually be identified by the ROM providing BASIC 4.0.) Candian/U.S. ROMs set a 60 Hz refresh rate; European ROMs set a ...
Non-CRTC PETs (Original PET, early 30xx) are fixed to 60 Hz.
CRTC (6545) based PETs (40xx/80xx/8x96/9000 - *1) use screen refresh rates set by its ROM (*2). 50 Hz for European machines, 60 Hz for US/Canadian units.
Regarding the details:
For the European models there was no need for compatibility with European television standards as far as I'm ...