Direction for the tri-dome insert in an Orthophonic Reproducer?

[Dischoard]

So I thought this would be something I could easily find googling pictures but alas, the internet is just as confused as I am (and often neglects to take pictures of the part I'm looking for).

Just picked up a VV 4-7 and I have replacement back rubber flanges and sat down this morning to install them. That's when I noticed that the thin metal tri-arm dome insert that fits below the flange is installed differently on both of my reproducers. So which was is correct? Up or down? Or does it even matter?

This:

Or this:

[Dischoard]

Oh, and does anybody have suggestions for a spanner tool to get the spanner ring off the Orthophonics? I'm going to start working on some wrecked examples to get some experience and have long ago found that cobbling together a bunch of the wrong tools is a poor substitute for finding the one right tool...

[Inigo]

I don't know, but the one cupping towards the diaphragm seems to be able to touch it if the vibration is strong enough!

[Dischoard]

That sounds like one vote for facing up!

[physicist]

But what is the purpose of the dome? If it is to protect the diaphragm from damage through excessive displacement, then it needs to face in. Can anyone explain what it's for if it's facing the other way?

[OrthoFan]

But what is the purpose of the dome? If it is to protect the diaphragm from damage through excessive displacement, then it needs to face in. Can anyone explain what it's for if it's facing the other way?

If you do a google image search -- https://www.google.com/search?q=Orthoph ... 5&dpr=1.54 -- you'll see that all of the sound boxes with the flat spring style inset show it bowing outward away from the diaphragm. If it's bowed inward, it may touch the back of the diaphragm, causing distortion. I'd imagine that was put there to protect the fragile diaphragm from damage; to keep some nimrod, or child, from ruining the diaphragm should he carelessly stick his finger into the throat.

It's the tiny stop-screw on the front of the sound box that protects the diaphragm from damage if the needle-bar's thumbscrew is roughly tightened. (A compliant diaphragm will flex slightly when the thumbscrew is tightened.) The tiny screw should be adjusted carefully--initially tightened so it just touches the needle bar, and then unscrewed a couple of turns so that no contact is made.

The flat spring style insert in the throat of the sound box was eventually phased out in favor of a pot-metal ring with a bullet shaped cone in its center, or "Phasing Plug."

SEE: viewtopic.php?f=2&t=17719
ALSO: viewtopic.php?f=2&t=23070

The phasing or phase plug increased the impedance of the sound box, and supposedly enhanced its performance.

OrthoFan

[MarkELynch]

The earliest Orthophonic reproducers had no guard in the throat, the stamped domed guard we are discussing here was added next, in the last version, as noted by Fan, the guard was incorporated with a bullet shaped phasing plug. I suspect the guard was used to prevent curious fingers from damaging the diaphragm or perhaps to prevent diaphragm damage by users trying to mount an Orthophonic reproducer in place of a #2 or Exhibition. The earliest U-tube having a smaller diameter than the Orthophonic type.

As suspected, the domed insert is intended to be installed with the convex side facing out. Here is a patent drawing by Victor’s chief physicist, Dr Haigis, picturing the insert. Notice the alternate needle bar mounting using flexible members in place of the ball bearings. As far as anyone knows this design and other needle bar mountings that were also patented were never implemented in production.

Mark

[Curt A]

Oh, and does anybody have suggestions for a spanner tool to get the spanner ring off the Orthophonics? I'm going to start working on some wrecked examples to get some experience and have long ago found that cobbling together a bunch of the wrong tools is a poor substitute for finding the one right tool...

A simple "spanner tool" can be made out of a piece of wood with two small nails driven in - spaced to align with the two holes in the ring. Cut or grind off the heads after driving them in, so they fit into the holes...

[Dischoard]

Thanks Mark, that diagram is perfect!

And thanks for the suggestion Curt, I imagine it would have to be a strong piece of wood given how tight these things are, can't wait to experiment!