Choirboy getting three times as much (6)
I believe the answer is:
treble
I believe this clue is a double definition.
'choirboy' is the first definition.
(I've seen this before)
'three times as much' is the second definition.
(I've seen this before)
'getting' acts as a link.
(Other definitions for treble that I've seen before include "boy in church choir" , "large measure" , "Three times - a boy soprano" , "High voice; occurring three times" , "High boy's singing voice" .)