Hard American musicians to manage carefully (7)
I believe the answer is:
husband
'manage carefully' is the definition.
(I've seen this before)
'hard american musicians' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'american' becomes 'US' (abbreviation for United States).
'musicians' becomes 'band' (group of musicians).
'h'+'us'+'band'='HUSBAND'
'to' is the link.
(Other definitions for husband that I've seen before include "Make careful use of" , "Partner in marriage" , "Man United" , "M arried man" , "be economical" .)