Wax cylinder recorder (5)
I believe the answer is:
taper
I believe this clue is a double definition.
'wax cylinder' is the first definition.
(taper is a type of candle)
'recorder' is the second definition.
(I've seen this before)
(Other definitions for taper that I've seen before include "Narrow towards the end" , "Prate (anag.)" , "Peter out" , "Become thinner towards one end" , "Wind down" .)