Once volunteers bother to share a PA system (6)
I believe the answer is:
tannoy
'system' is the definition.
(I have seen 'Sound system ' mean 'tannoy' so perhaps 'system' could also mean 'tannoy')
'once volunteers bother to share a pa' is the wordplay.
I cannot quite understand how this works, but
'volunteers' could be 'ta' (abbreviation for Territorial Army) and 'ta' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tannoy that I've seen before include "Orator's amplifier" , "Loudspeaker system" , "Public-address system" , "Speaker" , "Sound amplification system" .)