Though notedly valuable, not the complete instrument (5)
I believe the answer is:
strad
'instrument' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for strad that I've seen before include "fiddle exposed" , "Famous violin" , "Noted violin" , "Valuable violin (colloq.)" , "musical instrument" .)