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Here also is a pdf of "The Mechanics of Soundboxes by Peter Heath". It's also from the Hillandale News but from issue 227 Autumn 1999 not Spring as mentioned in the article.

Hi chunny. Thanks for the pdf to Peter Heath's soundbox article. He is certainly a technical sort of chap!
Here is my answer to the "Balmain" horn carriage-a gliding cloud!

Brilliant again Alastair! Seriously, there could be something in that idea, in a room with a very high ceiling - perhaps Graham's music room? Wink, wink!

It would be huge fun to experiment with the Montgolfier-Balmain gramophone. No shortage of hot air around here......

Oops, I wasn't thinking of hot air! Rather, suspending the horn from a very high beam, in lieu of the mercury baths or rails - leaving only the lateral (needle track) restraint required.

Hi Graham and Andy-great Idea, I never thought of suspending the horn from Graham's ceiling!!

The article by Peter Heath in the last part, disassembling of the soundbox, making a new diaphragm and reassembling, reveals some interesting points. First, he seems to use a jammed soundbox, as he needs to force the front ring out from the backplate by tapping with a screwdriver. In my case, I did a different thing... Fearing to force and break the sb, I decided to carefully cut the front ring using a dremel tool with a saw disc. I chose a point in the middle section between two of the four screws, in the upper part of the sb, far from the needlebar fulcrum, and I cut a radial groove at the front, until I reached the backplate, cutting through the entire thickness of the front ring. Then continued by the side of the front ring. Naturally I also had to cut the groove through the backplate knurled lip. This way I managed to free the front ring from the backplate. A click was produced when the groove ended cutting the ring completely, when the stress was relieved. Disassembling was now free from stresses. Next I grinded and polished around the backplate ridge that engages into the front ring, pressing the diaphragm edge in place when assembled. Then I reassembled the front ring in place on the backplate (with the diaphragm removed), but interspersed a strip of paper just under the groove I'd made. I screwed all in place, to be sure everything was in position, and refilled the front ring groove with metal epoxy cement. Thus I restored the front ring integrity, ensuring that the sb can now be disassembled and reassembled perfectly, under no stress. Later the paper strip was removed, it's mission being only to act as a backing mold for the glue, avoiding it to spread under the ring and adhering it to the backplate forever!
I've also noticed that the backplate follows the shape of the diaphragm, and so it could probably be used as a backing mold to press an aluminium sheet against it and form a new diaphragm.
I didn't understand very well what he refers to as "circular dimples" formed on the diaphragm edge instead of the diagonal corrugations of the 5a or the diamond shaped triangular ridges of the 5b. Probably he's referring to those diaphragms that have instead a pattern of consecutive C shaped grooves all around the diaphragm edge, which Indeed seem much easier to make by hand.
I have to try that myself...

There is a guy in England, John Street I think he is called who makes replacement backs in aluminium for the HMV 5A and 5B. In the event that you break one of those dreadful mazak backs that they come with.
I butchered mine when I attempted to get it apart so he was my only recourse.

Thanks, Daithi. I know about those backplates, and the man is John Sleep, 'The Gramophone Man', at West Pentire, i believe. I've bought something from him years ago, maybe any parts, or records... But the backplates he's made have a different back collar, as it's made so it fits directly in the tonearm, with 'no need of that perishable rubber collar'...! This I believe might be a fatal error... The rubber collar is depicted as a disturbance from which these new plates get rid off...
Indeed it is a fundamental part of the mechanical impedance chain, and must not be ignored, absolutely! The compliance at the back of the soundbox is needed, together with the SB body mass, to decay the vibrations transmitted from the needlebar support to the SB body, then through its body mass and the collar compliance, to the tonearm body. These vibratioins are indeed a leak of energy from the main source (needle) to the SB body instead of going to the diaphragm, and this is a part of the circuit (I suspect it was never represented in the Percy Wilson's circuit schemes in Gramophones and Electrical Reproducers, 1929) which derives part of the needle energy out of the diaphragm.
So the impedances there, as said, must not be changed. Probably the difference of having a rubber collar or not are only noticeable to the finest ears, but there will be a difference, of course. Think that fine-eared gramophonists and mechanical tinkers use to test rubber collars of different compliances, finding different SB responses when changed. I believe the bass transmission to the diaphragm is what suffers most in sound production if the joint at the abck of the SB is stiff. Besides that, part of the vibration energy migrating through this path, in absence of the rubber, is reflected back to the needle point, causing more wear to the grooves. Then annoying resononances at some notes can reach the needle, wearing or breaking the grooves very fast if the sympathetic note is being reproduced.
So IMHO, these new backs, precious and very good otherwise, are marred because of this happy idea of supressing the space for the rubber collar. They should be repeated but with their true dimensions, as the originals. I'm sorry for John, otherwise a very kind man and helpful, but I would never install one of those backplates as they are... They need some work at the back collar to open the inner diameter to the dimensions of the rubber collar. With a lathe at hand, this would be a very easy modification to do...