If you really have a Thorens TD 125 (ab) with the original arm, you have a rarity. The arm is a TP-25
http://www.thorensinfo.de/assets/images/TP25.jpg
with TP50 headshell. Unfortunately, there isn't much info on this arm. I'd say it's a medium mass arm which should work fine with 'normal' cartridges. The TD 125 however deserves a (much) better arm, so plenty of room for improvement there.
http://www.thorensinfo.de/assets/images/TP25.jpg
with TP50 headshell. Unfortunately, there isn't much info on this arm. I'd say it's a medium mass arm which should work fine with 'normal' cartridges. The TD 125 however deserves a (much) better arm, so plenty of room for improvement there.