Did you check the fuse rating? [Linked Image]

Dares one guess that the cable is 2.5 mm2 APPV? Did it have any markings?

Here is a little information about the Russian wire broadcasting system:

...practically all urban and rural houses was equipped by the original telco-based wire broadcasting system. It was intended for receiving from 1 to 3 radio channels with a simple cheap receiver, and the 1st channel was able to receive with the cheapest device (so-named “radio-point”) containing only a speaker, a transformer and a volume control, without need of any additional power source. The reason why the telco gave the much attention for the broadcasting service was the civil defense. The wire system is able to function at the hard conditions such as air radio interferences and a power failure at the customer’s location.
Source: www.telephonetribute.com/international.html