Pamela,
I've done a quick check through my old reference books and can't find that particular Grundig model listed, but then it might not have been sold here in the U.K.
You really need the cartridge details, or maybe remove the old stylus assembly so that one of these specialist places can identify it for you.
Remember to get the correct type of stylus, or combination of turnover styli, as using the incorrect type can cause irreparable damage to a record.
The "standard" type for playing 78 r.p.m. records generally has a tip radius of 2.5 to 3.5 mil.
A "microgroove" stylus (LP/45) has a 1-mil tip for mono, and generally a 0.5 to 0.7-mil tip for stereo (or an elliptical tip, although this wasn't common on anything but very high-quality equipment in the 1960s).
By the way, many of the early mono crystal/ceramic cartridges do not have sufficient vertical compliance for playing stereo records and can damage them. Most of the mono cartridges made by the later 1960s were designed to be "stereo compatible."
