An extremely good read

Share your phonograph repair & restoration techniques here
Post Reply
User avatar
poodling around
Victor V
Posts: 2140
Joined: Tue Feb 20, 2018 11:52 am

An extremely good read

Post by poodling around »

I came across this, this evening.

I have only read a little of it so far - the tone-arm section - which is fascinating. (So, the needle should meet the centre of the turntable !).

When you have a few spare moments perhaps have a read too.

http://www.gramophonemuseum.com/images/ ... s-1929.pdf

CarlosV
Victor IV
Posts: 1835
Joined: Sun Mar 15, 2009 6:18 am
Location: Luxembourg

Re: An extremely good read

Post by CarlosV »

Indeed a good book, I have it in paper. Percy Wilson is probably the most famous specialist in the UK, his principles were used to design EMGs and Experts, the dust-mat record cleaner (that side arm with a nylon brush and a roller) in the 60s, and the whirl-based Loricraft record cleaner.

User avatar
Orchorsol
Victor IV
Posts: 1621
Joined: Wed Feb 22, 2012 9:03 am
Location: Dover, UK
Contact:

Re: An extremely good read

Post by Orchorsol »

poodling around wrote: Thu Jan 28, 2021 5:13 pm (So, the needle should meet the centre of the turntable !).
That's only for certain (most/earlier) designs of tonearm, not all.
BCN thorn needles made to the original 1920s specifications: http://www.burmesecolourneedles.com

Youtube channel: https://www.youtube.com/channel/UCe4DNb ... TPE-zTAJGg?

User avatar
poodling around
Victor V
Posts: 2140
Joined: Tue Feb 20, 2018 11:52 am

Re: An extremely good read

Post by poodling around »

Orchorsol wrote: Fri Jan 29, 2021 4:15 am
poodling around wrote: Thu Jan 28, 2021 5:13 pm (So, the needle should meet the centre of the turntable !).
That's only for certain (most/earlier) designs of tonearm, not all.
Very interesting.

Could you please explain / elaborate. I would be extremely grateful.

Thank you Orchorsol.

User avatar
Inigo
Victor VI
Posts: 3753
Joined: Mon Dec 18, 2017 1:51 am
Personal Text: Keep'em well oiled
Location: Madrid, Spain
Contact:

Re: An extremely good read

Post by Inigo »

You should read it deeply. That case of needle falling in the spindle is an example of bad design, regarding the alignment. Further he explains that the solutions for good alignment unavoidably lead to a situation where the needle falls in front of the spindle, i.e. it passes away the spindle by a given distance, small, that is called overlap. This overlap benefits the tracking, well, it is indeed a consequence --unavoidable-- of a good tracking design, but also has a drawback: it increases the lateral force caused on the tonearm by the friction of the grooves against the needle, towards the centre of the record. The solution for this is to produce a lateral compensation of this force by means of the counterweight named anti-skating on modern turntables, which in fact introduces a lateral force on the tonearm outwards. In gramophones this can be arranged by giving a gentle slope to the motorboard or the entire machine towards the edge of the record, using the lateral component of gravity force. When you place the needle on the runout area around the label of the record, with the record spinning at 78rpm, the needle should stay in the same place, not moving aside. This is very complex, for the force needed is variable across the record. When you put the needle on the blank area before the first groove, the lateral component of that friction is who pushes the needle into the first groove.
The most dangerous situation is at the end of the record, where this force tends to push the needle into the label. I use to arrange the equilibrium so that in the inner blank area around the label, the needle stays in position, or even had just a small tendency to return to the last groove. I've found this equilibrium to be the safer situation.
---
No merit at all by my side; I've studied Wilson's book very deeply, and still continue studying it. I've also been immersed in the maths about this problem by myself, before discovering that book! But in all aspects Wilson's book was a revelation when I acquired it many years ago!
Inigo

User avatar
poodling around
Victor V
Posts: 2140
Joined: Tue Feb 20, 2018 11:52 am

Re: An extremely good read

Post by poodling around »

Inigo wrote: Fri Jan 29, 2021 8:02 am You should read it deeply. That case of needle falling in the spindle is an example of bad design, regarding the alignment. Further he explains that the solutions for good alignment unavoidably lead to a situation where the needle falls in front of the spindle, i.e. it passes away the spindle by a given distance, small, that is called overlap. This overlap benefits the tracking, well, it is indeed a consequence --unavoidable-- of a good tracking design, but also has a drawback: it increases the lateral force caused on the tonearm by the friction of the grooves against the needle, towards the centre of the record. The solution for this is to produce a lateral compensation of this force by means of the counterweight named anti-skating on modern turntables, which in fact introduces a lateral force on the tonearm outwards. In gramophones this can be arranged by giving a gentle slope to the motorboard or the entire machine towards the edge of the record, using the lateral component of gravity force. When you place the needle on the runout area around the label of the record, with the record spinning at 78rpm, the needle should stay in the same place, not moving aside. This is very complex, for the force needed is variable across the record. When you put the needle on the blank area before the first groove, the lateral component of that friction is who pushes the needle into the first groove.
The most dangerous situation is at the end of the record, where this force tends to push the needle into the label. I use to arrange the equilibrium so that in the inner blank area around the label, the needle stays in position, or even had just a small tendency to return to the last groove. I've found this equilibrium to be the safer situation.
---
No merit at all by my side; I've studied Wilson's book very deeply, and still continue studying it. I've also been immersed in the maths about this problem by myself, before discovering that book! But in all aspects Wilson's book was a revelation when I acquired it many years ago!
I see. Thank you very much Inigo.

I am just in the very initial stages of 'doing up' an old portable gramophone - the tone arm seems original as there are only the three original screw holes in the board. But the needle shouldn't be as far back from the centre spindle as this should it ? (Photograph below).
Attachments
middle.jpg
middle.jpg (181.48 KiB) Viewed 1404 times

User avatar
emgcr
Victor IV
Posts: 1086
Joined: Mon Jul 02, 2012 9:57 am
Location: Hampshire, England.
Contact:

Re: An extremely good read

Post by emgcr »

Richard, you have discovered our "Bible" ! Percy Wilson was the grand master in this area and this book has never been bettered.

You may find this thread of assistance ? "Offset" and "overlap" are the main keys to correct tracking and geometry.

viewtopic.php?f=11&t=15253&p=88350&hili ... ing#p88350

Your photo shows an impossible tracking situation in my view. Something is wrong...........

User avatar
poodling around
Victor V
Posts: 2140
Joined: Tue Feb 20, 2018 11:52 am

Re: An extremely good read

Post by poodling around »

emgcr wrote: Fri Jan 29, 2021 8:26 am Richard, you have discovered our "Bible" ! Percy Wilson was the grand master in this area and this book has never been bettered.

You may find this thread of assistance ? "Offset" and "overlap" are the main keys to correct tracking and geometry.

viewtopic.php?f=11&t=15253&p=88350&hili ... ing#p88350

Your photo shows an impossible tracking situation in my view. Something is wrong...........

Yes, it is odd. The case is the same length as an HMV 101 - the tone-arm is very similar too and the turntable is a 10 inch standard one. However, where the tonearm was 'factory fitted' to meet the internal horn (which is also like the HMV 101's) is about 2 inches further away from the turntable than the 101. This seems to have created the 'impossible tracking situation'.

I keep thinking, as everything seems original and 'factory fitted', then this is very odd.

Post Reply