Well, they are both 100KHz calibrators and they both use the same tube (6AU6). And, I think the schematic is the same. The HA-7 used a tube type crystal and the HA-19 used a standard crystal. So if the plugs are the same and are wired the same, I would give it a try.Here is a link to a QRZ discussion showing what someone did about the lack of a HA-7.