Meltrope III Diaphragm attachment to needle bar

[contessa]

While searching for information on Meltrope III rebuilding, I have found out that its diaphragm assembly also consists of subsidiary parts that should be equivalent to the 'spider' of an Orthophonic soundbox.

The diaphragm was designed to be sandwitched between 2 of these 'spiders'.

My questions are...

1. Should the 'spiders' be attached to the diaphragm? If so, should these be glued on with some sort of adhesive, wax, or instead, be soldered?

2. How were the diaphragm and the 'spiders' connected with the needle bar?
a. Only the 'spiders' were connected with the needle bar.
b. Only the diaphragm was connected to the needle bar.
c. Both the 'spiders' and diaphragm were connected with the needle bar.

3. Which kind of adhesive should be used for connecting the diaphragm, or the 'spiders', to the needle bar?

[HMV130]

Can you provide a picture? So one can identify the model.

[contessa]

Can you provide a picture? So one can identify the model.

Well, this is the soundbox I am working on. Please let me know if more pictures are needed.

Thanks!

[HMV130]

Thank-you for the picture. Sorry I should have specified a picture of the diaphragm.

It is a late Mod. III so yes it should have what is called a spider but it doesn't look like the one in HMV mod.5A/B or Victor.

Do the diaphragm and stylus bar need any intervention?

[Inigo]

Hello.
By my own experience disassembling one of those, I can say that the two spiders are no more than two small aluminium domes that go either side of the diaphragm, that is sandwiched between them. These domes are simple copies of the central (small) dome of the diaphragm, and seemed to me to be made of the same material and thickness as the diaphragm. They are designed to cover that central small dome.
The needlebar has a rectangular pin that goes through corresponding rectangular holes in the first spider, then the central dome of the diaphragm and then the other spider, and at the back side, it has a machine pressed end which holds them three together. It could have had some lacquer bonding between them, but in my example it wasn't there, the spiders and diaphragm being a bit loose between them.
The general semblance of the set makes one think that the sole intention of the so called spiders was only to reinforce the small central dome of the diaphragm, not distributing the needle vibrations through several points around the diaphragm as they did in the orthophonic soundboxes or in the Bettini diaphragms.
Actually I managed to disengage the needlebar and disassemble the diaphragm, by careful grinding out the needlebar stamped end with the aid of a Dremel tool. I tested other diaphragms made by me, and did other experiments trying to improve the sound of my example, which muffled the treble somehow. Finally I reassembled it again using the original parts, and resealed the needlebar end to the spiders and diaphragm using Loctite glue.

[contessa]

Thank-you for the picture. Sorry I should have specified a picture of the diaphragm.

It is a late Mod. III so yes it should have what is called a spider but it doesn't look like the one in HMV mod.5A/B or Victor.

Do the diaphragm and stylus bar need any intervention?

Ah, I see. here are the pictures of the diaphragm and 'spider'.

And yes, the diaphragm mechanism needs attention, for one of the 'spiders' are missing. Perhaps I should replicate one by myself!

[contessa]

Hello.
By my own experience disassembling one of those, I can say that the two spiders are no more than two small aluminium domes that go either side of the diaphragm, that is sandwiched between them. These domes are simple copies of the central (small) dome of the diaphragm, and seemed to me to be made of the same material and thickness as the diaphragm. They are designed to cover that central small dome.
The needlebar has a rectangular pin that goes through corresponding rectangular holes in the first spider, then the central dome of the diaphragm and then the other spider, and at the back side, it has a machine pressed end which holds them three together. It could have had some lacquer bonding between them, but in my example it wasn't there, the spiders and diaphragm being a bit loose between them.
The general semblance of the set makes one think that the sole intention of the so called spiders was only to reinforce the small central dome of the diaphragm, not distributing the needle vibrations through several points around the diaphragm as they did in the orthophonic soundboxes or in the Bettini diaphragms.
Actually I managed to disengage the needlebar and disassemble the diaphragm, by careful grinding out the needlebar stamped end with the aid of a Dremel tool. I tested other diaphragms made by me, and did other experiments trying to improve the sound of my example, which muffled the treble somehow. Finally I reassembled it again using the original parts, and resealed the needlebar end to the spiders and diaphragm using Loctite glue.

I pay respect to your braveness to go all through the burden!

I find it quite odd, the diaphragm and spiders not being glued onto the fulcrum.

I wonder if other examples would have any adhesive between them.

Thank you for sharing your experience!

[emgcr]

May we have a photograph of the other (hidden) side of the diaphragm please ?

[contessa]

May we have a photograph of the other (hidden) side of the diaphragm please ?

These are the both sides of the diaphragm.

[emgcr]

Ah, many thanks. The reason I asked to see both sides is because we have an ongoing and unsolved mystery regarding some of the (later ?) diaphragms which have an extra section with annular rings on the reverse side. If you would like to look at the following thread you can see what I am talking about (scroll down on page 3):

viewtopic.php?f=11&t=33157&hilit=Meltrope&start=20

So, the diaphragm with the added section therefore has four parts---one large and one small with annular rings and one "spider" or "dished washer" on either side. They were pressed and then riveted together. To date, nobody has quite been able to explain why they did this or what the effects might be. Additionally, it is unknown whether or not any form of glue or anti-rattle material was interposed. From investigations to date it would appear that they were just bare and pressed/riveted---job done !

Looking at the photos, yours does not seem to be in this category and should, therefore, only have three parts.