Hi Tim,
Use this link, scroll down to Heathkit DC-100 Modulation Trans:
http://www.harbachelectronics.com/_mgxftp/pwdamateur/PWDAMATEURH.PDFEDIT: Believe that you are on dial-up, but I should probably not copy and paste the info here, as think that this info is probably under copyright.
This transformer question sounds like trouble, hope that this is a not because you need a new one.
72 GL, Vic