Singer's number goes gold (5)
I believe the answer is:
tenor
'singer's' is the definition.
(tenor is a kind of singer)
'number goes gold' is the wordplay.
'number goes' becomes 'ten' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'ten'+'or'='TENOR'
Can you help me to learn more?
(Other definitions for tenor that I've seen before include "High voice - low bell" , "Male 17" , "General drift or meaning" , "Eg, Placido Domingo" , "thread" .)