Melody right for radio (5)
I believe the answer is:
Here is my best explanation:
'radio' is the definition.
('tuner' can be a synonym of 'radio')
'melody right' is the subsidiary indication.
'melody' becomes 'tune' ('tune' can be a synonym of 'melody').
'right' becomes 'r' (common abbreviation).
'for' is the link.
(Other definitions for tuner that I've seen before include "Adjuster of pianos", "Radio adjuster", "Radio receiver", "Piano adjuster", "piano man?" and "Motor specialist".)