Head of conservatoire appearing again on radio, playing instrument (9)
I believe the answer is:
accordion
'instrument' is the definition.
(accordion is a kind of instrument)
'head of conservatoire appearing again on radio playing' is the wordplay.
I cannot really understand how this works, but
'of' could be 'o' and 'o' is found within the answer.
'appearing' could be 'on' (e.g. on stage or on television) and 'on' is found within the answer.
This explanation may well be incorrect...
(Other definitions for accordion that I've seen before include "It's played" , "Bellows-operated instrument" , "squeeze it while operating keys" , "Squeeze box" , "Free-reed aerophone" .)