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Thanks for the advice and pointing me to the post by Ian Maxted. It gives me the confidence to experiment with some gentle tweaking after replacing the gaskets.
Would the small setscrews all be BA threads?
Iain

I am not sure which soundbox you are dealing with but, in respect of the EMG 4-spring box, the machine screws thread size securing the leaf springs which bear onto the stylus/needle platform is 8 BA, whereas the thread size for the adjoining back piece to the main casing is 9 BA (yes, the wrong way round you might think !). The three holes in the casing are through-drilled and threaded all the way thus the securing counter-sunk screws for the front triangular stylus guard are also 9 BA.

Good luck with your adjustments which I think you will come to enjoy although there are likely to be a few frustrations along the way too ! That is the nature of the beast for all of us I am afraid !

There was a debate a few years ago about the purpose of the two pegs which appear on some EMG 4-spring soundbox examples on the back of the main case. These are definitely non-metallic but seem to be made of some strong composite material similar to (but not) Tufnol. The only reason for these that I can think of is to take the torque generated when mounting the soundbox onto the tonearm. The strength of the three 9 BA brass set screws joining the two halves of the case is not really adequate for that purpose so great care must always be taken when twisting, particularly if the gap between the two halves is great. Non-metallic is clearly to prohibit unwanted vibration and sounds. The pegs are usually a reasonable push-fit in their counterparts and may be a little short in the example shown in the photo---or the gasketing is an unusually large diameter. From the soundboxes I have seen these are only found in a minority of (later?) examples and have often been cut off by subsequent owners---for what reason I know not but possibly because they thought they might interfere with the delicate pressure adjustments ? Strange, but people have different opinions and ideas..............

My EMG 4 spring still has those present, I'd have thought they may have been to ease alignment when putting the soundbox together and lessen the risk of cross threading and perhaps act as guides when adjusting the soundbox back, it's all anybody's guess though!

Thanks for the advice Graham, the soundbox that came with my Mk VIII is the exhibition type with mica diaphragm. Although the flyers that Chunny posted indicate the gramophone was originally supplied with two soundboxes the 2nd probably parted company with the machine long before I acquired it. The soundbox I have has the Meltrope type back so hopefully will be secured with BA setscrews.
Looking through this forum over the past couple of weeks has convinced me that the aluminium diaphragm EMG soundboxes are rarer than hens teeth and very very expensive if and when they do crop up.

Thank you Iain. May we have a photo or two of your soundbox please ?

A couple of pictures of soundbox as requested by Graham

Wonderful to see, many thanks Iain! I have one very similar, possibly almost identical, but with an aluminium diaphragm which it probably didn't have at the start of its life. The same style of EMG lettering was only revealed when I took it apart to rebuild it.

Thanks to all for the continuing contributions in this fascinating thread!

Many thanks Iain and it is fascinating to see the development process. The first three photos below show my version of your box but with an aluminium diaphragm and interestingly also depict the original interposed fibre washer to prohibit the tonearm from coming into direct contact with the main body of the soundbox mentioned by Alastair earlier in the thread. Of note also is your aluminium needle holder---mine is brass. Is yours pierced in a triangular fashion for bamboo ? Mine is not. From memory (it is ten years since this box was rebuilt) the EMG engraving does not appear inside on the back-plate.

The remaining four photos go on to show the next development with the advent of the hooped and finely-pointed springs but still with mica diaphragm and cylindrical bore for thorn or steel needles only. The cardboard box in which this one came emanated from High Holborn and was marked as to be used for steel needles. The rather beautifully stylised two "S"s in black ink might have been drawn by EMG themselves with the pencil "teel needles" having been added by the purchaser subsequently ? It is also worth observing the rounded and artistic "m" in the EMG logo---quite different to the brass engraving. I have always thought the date to be 1927 but I could be wrong ? The patent references in both cases on the back-plate mention 1927 but that, of course, would also be present on later examples. This example came from the Roger Thorne estate at auction in July 2011.

Graham thanks for your photos. Here are a couple of pictures, showing the chuck for holding fibre needles and also the attachment for the springs. I note that (as per Exhibition box) the two springs are secured on the needle bar and the other end, under the head of the set screw, has a slightly oversize hole to allow for movement. The lock nuts on the set screws are tightened against the lugs on the body so the spring is held under the screw head by its own tension. It appears on your example with the curved springs which press against the underside of the needle bar that the spring is secured between the lock nut and the body lug. Is this correct and is there a current source for replacement springs of the curved type? Presumable the curved springs are a later refinement.
Iain