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Tracking error on an HMV 102 with a No 4 soundbox
http://forum.talkingmachine.info/viewtopic.php?f=11&t=32870
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Author:  Marco Gilardetti [ Tue Nov 14, 2017 9:51 am ]
Post subject:  Re: Tracking error on an HMV 102 with a No 4 soundbox

To help you visualize how far your 5B is from a 60° reading angle, I have superimposed the picture you provided with a sketch of a 60° angle.

I have also superimposed the images of the 5B and the 4 soundboxes; the image speaks pretty much for itself and clearly shows, by looking at the needlebars, that the two soundboxes approach the grooves at a significantly different angle.

Attachments:
N5B_60deg.jpg
N5B_60deg.jpg [ 115.93 KiB | Viewed 99 times ]
N4_N5.jpg
N4_N5.jpg [ 48.78 KiB | Viewed 99 times ]

Author:  shoshani [ Tue Nov 14, 2017 1:37 pm ]
Post subject:  Re: Tracking error on an HMV 102 with a No 4 soundbox

Marco, I see what you're saying, but also these are casual snaps from a handheld phone. The image isn't level, as can be seen in both of these images by the fact that the side of the gramophone slopes slightly upward from left to right. I can't do it right now because I'm at work, but in a few hours I'll take a new photo of the 5b at least, with my phone resting on a level surface.

Author:  shoshani [ Tue Nov 14, 2017 7:57 pm ]
Post subject:  Re: Tracking error on an HMV 102 with a No 4 soundbox

Okay, I took new pictures, both of them from as straight on as I could, lined up as similarly as I could.

Then I overlaid a 60 degree angle eps that I downloaded, changing the white background to transparent and changing the black angle line to red for easier visibility.

It would seem that neither soundbox sits with the needle at 60 degrees. I blame myself for the 4; I inserted the American ring and isolator, which has the bayonet pin integral to it, by eye. It's also in there too tightly to move. But the 5b was not only factory set, HMV isolator/ring assemblies do not have an integral bayonet pin. The upper set screw is actually the bayonet pin, going through the rubber and brass which are pre-drilled to pass it through.

Attachment:
5a-start-angle.jpg
5a-start-angle.jpg [ 265.36 KiB | Viewed 77 times ]

Attachment:
4-start-angle.jpg
4-start-angle.jpg [ 221.67 KiB | Viewed 77 times ]

Author:  Marco Gilardetti [ Thu Nov 16, 2017 6:08 am ]
Post subject:  Re: Tracking error on an HMV 102 with a No 4 soundbox

It is then confirmed that the two soundboxes approach the record at different angles, and in particular that the 5B approaches it at an angle that is not gentle with records.

I believe that 60 degrees has to be considered a sort of upper limit still quite OK but not to be exceeded, rather than the ideal one. I remember reading recently in the "Gramophone Tips 1927" that Capt. H.T. Barnett considered this angle harmful to the record, and suggested it to be reduced to 50°.

Author:  shoshani [ Thu Nov 16, 2017 7:54 am ]
Post subject:  Re: Tracking error on an HMV 102 with a No 4 soundbox

Marco Gilardetti wrote:
It is then confirmed that the two soundboxes approach the record at different angles, and in particular that the 5B approaches it at an angle that is not gentle with records.


I'm going to check this with a printout of the 60 degree angle directly against the needle, just to make sure what we're seeing isn't a camera parallax thing, but it would appear that this is the case. I've never seen any grit or powder on the needle or in the grooves, though, and I only ever use soft tone needles with it. (Anything larger than soft tone blows the house away.)

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