some Meltrope questions

[Inigo]

What a great thing would have been to make new backs for hmv soundboxes, providing them with the Meltrope adjustable system for the collar...

[IainW]

Another question for Meltrope type soundbox fittings can anyone confirm if the thread form for the back collar on Meltrope / EMG / Expert etc soundboxes are BSB 26TPI or something else? The answer probably lies in the forum somewhere but I have not managed to find it.
Iain

[emgcr]

1.25" X 24 TPI for Meltrope, EMG, Expert and Astra. Probably their own thread.

[IainW]

Aah, thanks Graham. If not BSB and cycle threads do not seem to match, the nearest I can find would seem to be a UNS thread with 60 degree profile. Is this correct?

[emgcr]

Hello Iain, I think that would be correct although I am not absolutely 100% certain about the 60 degree profile. I no longer have a shadowgraph so am unable to check. However, for all practical purposes I think 1.25" X 24 tpi UNS would be perfectly serviceable. May I ask what you are trying to do---cut new threads or clean up old ones ? Best wishes.

[IainW]

Thanks Graham, I have found myself a lump of brass in the garage and am toying with the idea of turning up a new back for one of the Exhibition look-a-like soundboxes.

[emgcr]

Sounds interesting. Perhaps share the result in due course ? Good luck !

[anchorman]

What a great thing would have been to make new backs for hmv soundboxes, providing them with the Meltrope adjustable system for the collar...

This is something that I plan to do at some point. I’ve got a meltrope III that I bought from Ahmed, just looking for a few more goodies to fill the package before I ask him to send it across from England. When I have that, I’ll measure the threads and make some pieces that are fully compatible with original meltrope parts and fit onto the No. 5, and No. 4 HMV soundboxes, and probsbly make ones to fit the various flavors of Columbia viva-tonal Soundboxes in my collection. I’m really tempted to also make orchorsol style backs also, so that various failings in arm geometry can be slightly compensated at the soundbox mount. But I’ve got only so much time and too many projects!

[anchorman]

Another question for Meltrope type soundbox fittings can anyone confirm if the thread form for the back collar on Meltrope / EMG / Expert etc soundboxes are BSB 26TPI or something else? The answer probably lies in the forum somewhere but I have not managed to find it.
Iain

If I can measure properly, I’ll post the thread angle when I get the meltrope in my hands. If your cutting your own threads it’s probably going to work to just make the female threads slightly oversized or the male part slightly undersized in diameter so that either the 55 or 60 degree thread profile would fit. It’s not very good engineering practice, but at the same time, the pressure involved is minimal, they’re not in constant motion, and there is the rubber isolator that will take up the slack/sloppiness in the threads as it is compressed.

[leels1]

It looks like someone has already done some mods to the Exhibition type soundboxes.

https://www.ebay.co.uk/itm/334600637506 ... media=COPY

Although the back seems to be original with the Meltrope type screw attached to it.

I had a play about with an Exhibition (this is a Saturn but more or less the same) trying to copy an early EMG. Fabricated some springs and made a back from some plumbing brass coupling. The thread pitch is totally wrong but was an experiment without a lathe! It’s also a little heavy I think but it works ok.

As you can see I remade a diaphragm from an annealed coke can (I put the ridges in the wrong way round in error so the front has the writing in still!), after measuring a lot of my Meltrope diaphragms it’s the same thickness but must be annealed to remove the springiness.

Sounds pretty good but the screws holding the springs need to be pretty tight to stop sideways movement (something that isn’t as much of an issue on a Meltrope II, or even III.