Beat with good old musical piece (5)
I believe the answer is:
tango
'musical piece' is the definition.
(I've seen this before)
'beat with good old' is the wordplay.
'beat' becomes 'tan' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'good' becomes 'g' (abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tan'+'g'+'o'='TANGO'
(Other definitions for tango that I've seen before include "uniform to follow" , "Dance; letter T" , "Dance; T (radio comms.)" , "Latin American dance (requiring two?)" , "Rhythmic movement" .)