Questions on Tonearm Geometry

[mrvic2]

Hello Everyone.
I've been posting about my new May-Fair Portable for the last few weeks, and I'm planning this to be the last post I make on it. I have two major questions, and one very minor one.
1).
I have been doing some reading on the BCN website, and it talks about making sure your tonearm is level, which mine very much isn't. If I try to place it down on the back of a victrola record, it basically races to the center. On the website, it does say to put some shims under the machine, so to try this easily, I just simply tilted my machine manually, and the problem only stopped once the machine was tilted at a ridiculous angle. I believe it isn't the turntable not being level for two reasons. One, simply because it seems to be flat, and two, when the tonearm is placed in its "needle changing position", it likes to swing over towards the opposite side of the machine, i believe this could be an indication that it isn't level.
2).
This next question revolves around a post i saw about black dust from records. One person (forgive me for forgetting the name) stated any amount of noticeable black dust was a problem. Of course, me being an overthinker, has left me to be wondering about if there is anything wrong with my machine. I have gotten an extremely small amount of black dust on almost every play on all of my machines, such a small amount I have trouble trying to measure it, less than one millimeter cubed, or probably about 1-2 grains of salt in the worst cases. In any case, this made me wonder about tonearm geometry. Below is a picture of what I have done to show how the needle tracks. The straight line is simply a tracing of the path the reproducer takes across the record, and the perpendicular lines are how the reproducer sits at the intersecting point. I believe you can buy discs that track this, but this was just a random 3am project I had.

Tonearm Geometry

The first thing I noticed from this is how out of line the needle is from the spindle, from what little I know, this seems to be a bad thing. But again, it's from what little I know, so i figure taking it here is smarter than trying to re-engineer the machine off of a whim. (speaking of re-engineering, how would I be able to fix this?)

3).
This is the minor problem.
The latches on this phonograph have a key which sadly has been lost to time. I was wondering if any of you would know what I should look for to find this key. I highly doubt it's any proprietary/specialty key, due to this being an offbrand that uses parts from different companies. The pictures should be below.

Latch Unopened

Latch Open

Latch w/ Ruler

Any help is appreciated. Thank you all for your time.

[Marc Hildebrant]

There is a lot of information available regarding the tone arm geometry. You can start by reading in the Radiotron Fourth Edition in the record section. This famous handbook is available online as a pdf file.

Marc

[JerryVan]

The first thing I noticed from this is how out of line the needle is from the spindle, from what little I know, this seems to be a bad thing.

...and this is why your tonearm drifts towards the center when you do your level test. The drag of the needle on the record, (even the smooth backside), will create a lateral force vector that will push the tonearm towards center. If you want your machine level... use a level.

[emgcr]

......this made me wonder about tonearm geometry......

Tracking is a big subject originally mastered by Percy Wilson for EMG in the nineteen-twenties and discussed many times in this forum. Here below is an introduction---please click on the images to enlarge. You may also like to refer to the immortal book " Modern gramophones and electrical reproducers" (alignment protractor--page 132) available on-line thanks to the generosity of Chunny in his wonderful Gramophone Museum : https://archive.org/details/ModernGramophones1929

[emgcr]

Here are the last four pages of the booklet :

[Inigo]

Thanks for this interesting booklet!

[emgcr]

My pleasure Inigo, thank you. I think it is often quite hard to find previous articles and discussion on important topics in the forum so repetition can be useful.

[Orchorsol]

Here's a printable document from which a Wilson protractor can be made.

[Lah Ca]

Thank you to everyone for this most enjoyable and useful thread.

With modern tone arms and head shells, stylus overhang can generally be adjusted to one of the popular schemes, Baerwald, Stevenson, DIN, or Loefgren (A or B). The fact that there are multiple schemes suggests that there is no "correct" scheme. What is correct is dependent upon tone arm geometry (length in particular)--not all schemes can be configured on some arm/head shell/cartridge combinations. Correctness is also dependent upon what style of music and format of record you generally listen to and upon your personal taste. The null points, where the arc of the stylus' movement across the record intersect a straight line from the spindle which represents the track of the cutting lathe, have to fall somewhere on that straight track. Where they best fall is a matter of some contention.

It would seem to me that the choices for needle overhang on a talking machine are generally none, the overhang having been predetermined/set by the engineers who designed the machine. The end user will have some limited options, depending upon the design of the reproducer and its interface with the tone arm. On some machines the rake angle of the needle can be adjusted, on others it cant. Needle length will also have some limited effect on overhang.

What can you do with an alignment protractor for a talking machine other than to check the engineering choices and skill (or lack thereof) of the designers and manufacturers of the machine? The tone arms cannot be moved because of their interface with horns. I dimly recall, however, that the tone arm length might be adjustable on some Brunswick machines but I could be very wrong here. And I suppose that on some machines it might be possible to reposition the motor (and thus spindle and platter) on the motor board but not without modification of the motor board and case.

[Lah Ca]

@mrvic2

With regards to the missing key, you might take the machine into antique shops, luggage repair shops, horologist shops--anywhere that might have a collection of antique keys. The key is unlikely to be complicated--the lock looks like a very generic luggage thing and there are often very few key variations for each model of these sort of locks (locks only keep the honest people out). If you can find a key that works or almost works, you might be able to buy it or take an impression. An old school locksmith should be able to fashion a replica.

While it may be nice to have a key to complete a machine, I have heard it said a number of times in Youtube videos that you should not actually lock your machines because the locks are old, and once having locked a machine it may not be possible to open it again easily.