[Arran]

Here is a schematic for a Grunow model 530, it looks like it came out of Beitman's:

http://radio.codegods.net/node/6340

That one is an AC/DC set, it says that the IF is 455, so you may likely feed the input in through the antenna connection in series with something like a .05 uf capacitor, or the grid of the #78 tube.
Regards
Arran