Blood of the Man Devil (or House of Black Death) is a 1965 horror film starring Lon Chaney, Jr. and John Carradine. That ought to be enough to get anybody to watch it. Once. Andrea King, Tom Drake, Dolores Faith and Sabrina were also in it. I've never heard the word "coven" pronounced as it is here.
Internet Archive has it online:
Reviews are in short supply, and none of the sites I usually quote have included this film. Wikipedia doesn't even have an entry for it.