The Tripods

The tripods is a series produced by BCC in the 80s based on the trilogy by John Christopher.
There are 2 seasons produced.
All episodes are published on this channel.
Please subscribe to watch them all!
https://www.youtube.com/channel/UCDYLWEP-lPx0242n5e3saaw?view_as=subscriber&sub_confirmation=1

I also recommend to read the 3 books (The White Mountains, The City of Gold and Lead, The Pool of Fire). 

Synopsis (IMDB):
Robots with 3 legs and a hemisphere on top, known as the Tripods, have conquered Earth and turned the human race into slaves by implanting everyone over the age of 14 with a mind-control device. 13-year-old Will Parker and his friends, however, plot to defeat the Tripods before they take over the whole world and Earth will be theirs.