The Talking Machine Forum — For All Antique Phonographs & Recordings

Common two minute reproducers: Automatic reproducer, Model B (early Gem), Model C
Common four minute reproducers: Model H, Model N, Diamond A
Common combination reproducers: Model K, Model O

Record Type Reproducer Type Why
Brown Wax (Soft, 2-minute) Automatic (or Model B for Gem) Lightweight reproducers like the
Automatic were specifically
designed for the softer, early
wax cylinders to prevent
damage.
Black Wax (Harder, 2-minute) Model C The Model C has a heavier
stylus and weight designed for
the harder 2-minute black wax
records, where the groove was
molded into the cylinder.
Black Wax or Celluloid (Harder, 4-minute) Model H The Model H is designed for
4-minute records, which are
harder and have a different
groove shape than 2-minute
records.
2-minute and 4-minute Combination Model K This reproducer has a switch
to change settings for either
2-minute or 4-minute records,
providing versatility.

There are a number of free articles on the Antique Phonograph Society website. You'll find this one answers your questions, including pictures:

https://www.antiquephono.org/#/collectiondetails/16

George P.