[Phono-L] Class M

[Mike Tucker]

For the technical minded.

I have occasionally wondered what was the purpose of the screw in the topworks castings, under the mandrel, on Class M phonographs.

Reading a copy of the 1893 "The Phonogram", I came across an article on "How to work the Phonograph" which noted that "if the belt slips, it needs tightening" and goes on "with a long-handled screwdriver turn the projecting screw under the mandrel a few times, which will press the body forward and tighten the belt.".

The Class M's I have seen either have no screw in place or the screw goes through the casting and doesn't connect to anything, so turning the screw does precisely nothing.

I must assume that there was some additional part which the screw butted against to enable it to move the topworks, but I cannot see how or where this would fit.

Can anyone enlighten me?