by Joe_DS »
Tue Jan 26, 2010 8:08 am
That's a nice sound box, and it should perform very well once the hardened gaskets are replaced.
The function of the gaskets was to isolate the diaphragm from the sound box casing, but it also gave the diaphragm some flexibility, allowing it to plunge, to a certain extent, as the needle & needle bar moved back and forth while tracking the record's groove.
The way it is now, only the very center of the diaphragm can respond to the movement of the needle bar. This produces a higher pitched tone than the sound box would have had originally. But more important, it also restricts the movement of the needle-bar and stylus, forcing the needle to ride the center of the groove, and scrape away the sides. Best to have these gaskets replaced ASAP. You'll be amazed at the difference once you do.
This, by the way, is very different from the Orthophonic sound box, in which the actual movement of the diaphragm is NOT dependent on the softness of the gaskets. Quite the opposite. The gaskets were designed to rigidly clamp the edge of the diaphragm, while isolating it from the sound box's shell. (All of the original Orthophonic gaskets I've seen have been paper backed rubber, and the rubber was still in good condition!)
The ability of the Orthophonic diaphragm to move back and forth is due to the corrugated ring on the diaphragm's outer edge. (If you insert a needle into a good condition Orthophonic sound box, and tighten the thumbscrew, you can actually see the diaphragm plunge at the point of the corrugated ring.) Any restriction placed on the movement of the needle bar is normally due to frozen or out of alignment ball bearings, which is why that's a good place for a (non professional) re-builder to start.
JDS