Tune by old name being broadcast (2,3)
I believe the answer is:
on air
'being broadcast' is the definition.
(I've seen this before)
'tune by old name' is the wordplay.
'tune' becomes 'air' (I've seen this before).
'by' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'name' becomes 'n' (common abbreviation e.g. on forms).
'o'+'n'='on'
'air' after 'on' is 'ON AIR'.
(Other definitions for on air that I've seen before include "Radio show might be" , "with audience?" , "Broadcasting studio sign" , "put out" , "Transmitting now!" .)