Roadie almost ruined set (5)
I believe the answer is:
radio
'set' is the definition.
(radio is a kind of set)
'roadie almost ruined' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'ruined' indicates anagramming the letters.
'roadie' with its final letter taken away is 'roadi'.
'roadi' with letters rearranged gives 'RADIO'.
(Other definitions for radio that I've seen before include "Wireless broadcast" , "Broadcaster" , "Communications receiver" , "Receiving device" , "broadcasting station" .)