Solo for boy on vibraphone at last (5)
I believe the answer is:
alone
'solo' is the definition.
(I've seen this before)
'boy on vibraphone at last' is the wordplay.
'boy' becomes 'al' ().
'at last' indicates one should take the final letters.
The last letter of 'vibraphone' is 'e'.
'al'+'on'+'e'='ALONE'
'for' is the link.
(Other definitions for alone that I've seen before include "Without anybody or anything else" , "Singly" , "Single" , "Isolated; exclusively" , "Lacking company, solitary" .)