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 Post subject: Re: Difference between HMV 101 and 102 'arm'
PostPosted: Fri Jun 07, 2019 2:10 pm 
Victor I
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 192
Location: Madrid, Spain
The 101 actual tonearm is the inner tube. What is an add-up is the outer tube with the slot for engaging the no4 soundbox. What hmv did when designing the new orthophonic soundboxes was to use a backplate with the same bore at the metal neck holding the rubber connector. Thus, the soundboxes are interchangeable, and the two types of rubber connector have exactly the same outer diameter, the difference being in the inner diameter that matches the tonearm external bore. You can improve the performance of the New Gramophones of 1925 adding the orthophonic soundboxes. I've tried on a127 using a spare 5A and it has become the resident soundbox, the improvement in bass and overall fidelity with respect the no4 soundbox begging quite impressive.

 Post subject: Re: Difference between HMV 101 and 102 'arm'
PostPosted: Wed Jun 12, 2019 3:12 pm 
Victor Jr
Joined: Fri Mar 17, 2017 2:52 pm
Posts: 31
Location: Chicago
I did exactly that with my pair of 109s. 8-) There is a very small factor that I did not consider, in that the needle chuck of the 5A is very slightly shorter than that of the No 4, and the pivot assembly is mounted very slightly higher. This slightly shortens the effective playing height of the 5A, and in turn pitches the soundbox a very tiny degree when the record is playing - the top looks slightly further out than the bottom, rather than the assembly being perpendicular. (This is because the swan neck joint pivots the soundbox up and down at an angle, rather than straight, so if it's higher or lower than "true", it affects vertical perpendicularity. Is "perpendicularity" a word? Must be, I just used it...)

It doesn't seem to have any adverse effects on records, and there's a noticeable sonic difference on later records. Much later records. One of my test records is an extra copy of a Woody Herman and the Third Herd 78 that was recorded in 1953. The bass on it was very good both with a 4 and the adapted 5A, but the midrange-to-high definition, especially on trumpets, was much clearer with the 5A. I now have a pair of 109s, either of which can be purposed for specific types or eras of records since one has a No 4 soundbox and the other a 5A.

EDIT: last night I took a level to the soundboxes, and to my great surprise the 5A was fully level. Zero. The No 4, however, measured 3 degrees off-axis.

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