Revolutionary American inventor needing little ordinary capital (6)
I believe the answer is:
ottawa
'capital' is the definition.
(capital of Canada)
'revolutionary american inventor needing little ordinary' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'inventor' becomes 'Watt' (Scottish inventor James Watt).
'needing' is a charade indicator (letters next to each other).
'little' indicates taking the first letters.
The first letter of 'ordinary' is 'o'.
'a'+'watt'='awatt'
'awatt' back-to-front is 'ttawa'.
'ttawa' after 'o' is 'OTTAWA'.
(Other definitions for ottawa that I've seen before include "Canadian capital" , "somewhere in Canada" , "N. American city" , "capital city" , "Canada's capital" .)