In my fantasy setting there are dwarves, inspired by the "stereotypes" and traits presented in Dwarf Fortress, and thus, partially inspired by the LotR lore.
It has the implications that dwarves use magic, but to an extreme extent, and even then, it's mostly for industrial usage of mining, refining, smelting, manufacturing and so on. My dwarves are practically on the brink of entering an industrialized era, rather being pre-industrialized like most traditional fantasy races.
Because of it, I started wondering, what inventions of the Industrial Revolution might be possibly practical to research, invent and manufacture for such a race, and the radio grabbed my attention.
For the record, my setting consists of multiple closed communities with varying tech level, from prehistoric to pre-WW1 era, meaning that the radio may already exist in this world. Thus, I can imagine dwarves obtaining a single radio, analyzing its mechanics, and replicating it.
1) What preconditions are necessary for such a community to be able to invent the radio? Assume an abundance of any kind of metal, and that electricity is not widespread but they have proficiency with it.
2) What are the conditions necessary for mass-manufacturing early 20th century radios? Again, assume abundance of metal, proficiency in electronics, but also the existence of the concept of factories: assembly lines, separation of steps, etc.
Related question: what are the possible obstacles for such actions to happen? E.g. lack of fine mechanics