Police are appealing for witnesses following the incident in Herbert Street, Spring Boroughs, on Saturday, April 2.
At about 9.30am, a woman and man knocked at the victim’s door and, when he opened it, the man barged in, holding a knife and demanding money.
He broke into the television meter and stole the cash from inside it.
The man is described as white, about 35 years old, around 6ft with a stocky build. He had very short, shaven hair. He was wearing a white T-shirt and blue jeans.
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The woman is described as white, about 25 years old, 5ft 6in with a skinny build. She had short black hair that was slicked back and was wearing a black tank top and blue tracksuit bottoms.
Witnesses, or anyone with information, should contact Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555 111.