OK I've racked my brains and tried every trick I know!!
This is the best I can do...extracted records from the IGI
Barnard (sic) RAPLH bapt 21 Feb 1682 at St Martin in Meneage
Father - John RALPHJohn RALPH or HELIGEY bapt 18 July 1689 at St Martin in Meneage
Father - John RALPH or HELIGEY( I found this elsewhere too written as RALPH (HELIGEY))
Doesn't look like illegitimacy as both father and son are carrying the alias - I also found this at the websit given in one of the posting above...
Martaine RICHARD married Jane RALPH alias HELEGE on 7 Feb 1685 at St Martin in MeneageCould be a sister of your John RALPH senior?? Might give you another angle to try??

Best of luck