Son in carriage originally operating reliable radio (10)
I believe the answer is:
transistor
'radio' is the definition.
(I've seen this before)
'son in carriage originally operating reliable' is the wordplay.
'son' becomes 's'.
'in' is an insertion indicator.
'carriage' becomes 'transit' (I've seen this before**).
'originally' indicates taking the first letters.
The initial letters of 'operating reliable' is 'or'.
's' put inside 'transit' is 'transist'.
'transist'+'or'='TRANSISTOR'
(Other definitions for transistor that I've seen before include "Semiconductor device" , "Electronic component" , "Electronic device" , "Radio" .)