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I wonder, how can this HMV number 4 soundbox fit an HMV 102 gramophone tonearm ?????

Was it originally made like this ? The back-plate does not look like an HMV 5a or 5b ?

Switch the isolator. That's it.

gramophone-georg wrote: Fri Jun 02, 2023 4:31 pm Switch the isolator. That's it.

I can see what you mean but I don't think it would be physically possible when looking at this one or indeed what has happened.

Hopefully others will comment too ?

I also notice that the back screws are larger than usual ?

gramophone-georg wrote: Fri Jun 02, 2023 4:31 pm Switch the isolator. That's it.

Just what you said!

There are thicker isolators that allowed a 5A or 5B to be fitted to a no. 4 tonearm and conversely thinner isolators that permit the no. 4 to fit a 5a tonearm. Admittedly the latter is not something you see everyday. Why would anyone want to put an older mica diaphragm soundbox on a younger tonearm designed for matched impedance and the aluminium diaphragm?

I have several Indian machines with the former combination which was no doubt seen as an Intermediate upgrade.

I have done it the opposite way many times- a No. 4 isolator into a No. 5 or No. 16 soundbox to upgrade an earlier machine that would normally take an Exhibition, No. 2, or No. 4. Outer diameter of the isolator is the same.

Rats !!!!!!!!!! Wrong again !!

Thanks very much gramophone-georg and steve for educating me with this !

Very interesting indeed !

Yes and it's funny to do these switching trials.. The no4 and the 5a/b have the same neck size so the isolators are perfectly interchangeable. I bet they did it so to ease old machines improvement by selling the new soundbox to users of the old mica no4 as upgrade...
I've done it many times myself, though I find the 5a a bit 'too powerful' for the small hmv horns of the 101 or the tabletop 127. For these the best improvement I've found is the Meltrope III.