Hi and thank you so much for your replies.

In fact, it comes from a card with 8 of them, and I have 2 cards. So, 16 in total.
It was taken from an avintage udio-video system, I think.
LEM was a French company that distributed microphones from various mfgrs and also transformers made by Melodium. The Melodium company is extinct now since about 25 years. No documents were saved due to the contentious nature of the termination. Most transformers were custom jobs. unless you can identify what piece of gear they come from, you need to evaluate them by yourself. The methods have been discussed here already. PRR and me have proposed two methods.
Would be happy to have the link of your two methods, thank you.