Greatly increase output of ducal art and equip … (13)

I believe the answer is:

quadruplicate

'greatly increase' is the definition.

'output of ducal art and equip' is the wordplay.
'output of' indicates an anagram (output of the anagrammed letters).
'and' means one lot of letters go next to another (I've seen this in other clues).
'ducal'+'art'='ducalart'
'ducalart' put after 'equip' is 'equipducalart'.
'equipducalart' is an anagram of 'QUADRUPLICATE'.

I've seen this clue in The Times.

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