The Talking Machine Forum — For All Antique Phonographs & Recordings

...what does it do?

I was changing the bearings in an Orthophonic soundbox recently, while talking with a friend who's a smart feller, and he said that though he's asked a few collectors what that little screw on the needle bar casing is actually meant to do, nobody seemed to know. Guides to restoring Ortho soundboxes, like Tim Graczyk's, say that it mustn't touch the needle bar. So it just kind of sits there, like not touching the needle bar is its whole purpose in life. Somebody here must know: what good is it? Of course in the interest of science I had to take it off and play a record without it -- no difference as far as I could tell. So what purpose does it serve?

I believe the screw is there to limit the outward motion of the needle bar in case the soundbox is accidentally dropped or otherwise mishandled. It would help prevent damage or separation of the bar from the diaphragm "spider."
Bob

Make sure that it does not touch the needle bar.

The proper adjustment is to set it so it just touches the needle bar, and then unscrew it about two or three turns.

OrthoFan

barnettrp21122 wrote:I believe the screw is there to limit the outward motion of the needle bar in case the soundbox is accidentally dropped or otherwise mishandled. It would help prevent damage or separation of the bar from the diaphragm "spider."
Bob

Yes. To prevent catastrophic damage to the diaphragm / spider if mishandled.

Huh -- thanks guys, never would have thought that was its purpose. After all these years, of course, drop a pot-metal soundbox onto a hard surface and the screw probably wouldn't do much good -- the whole thing would probably just shatter! Appreciate the info.

Cody K wrote:Huh -- thanks guys, never would have thought that was its purpose. After all these years, of course, drop a pot-metal soundbox onto a hard surface and the screw probably wouldn't do much good -- the whole thing would probably just shatter! Appreciate the info.

True, but it would take less of a shock to ruin the diaphragm.

Not so much the drop of the whole reproducer body ( you definitely wouldn't want to do that these days, especially to a pot-metal unit !), but more so to protect against excess deflection of the needle-bar, should the needle-end of things be subjected to excessive force that would push the needle towards the backside of the reproducer... without this limit screw, the needle-bar / spider could be torn from the diaphragm ?

Thanks, Frank, that explains it even better. The screw stops the possibility of the needle bar fulcruming too far. Makes sense that a couple sixteenths of an inch could make a big difference considering how tenuously the spider's attached to the diaphragm.

Bingo !