Mounting a Jelco Tonearm


This is from a good friend of mine who is having a dilemna mounting a Jelco Tonearm.  I hope someone is able to help:

" I've been trying to determine a foolproof method for accurately locating the hole for a tonearm in a plinth.   I think the pivot to spindle distance or the total effective length provided by Jelco is just wrong.    Everytime I mount this thing it seems like it's not quite in the position it should be so the cartridges sit 1) in the middle of the headshell and 2) line up nicely with the alignment grid.  I think one of the numbers is wrong. But which one, and by how much?


I actually have one of those Dennesen Soundtracktors.   Do you remember those?  They are basically an older, plastic version of the expensive, but very nice aluminum Dr. Feikert one.


There's got to be a simple, logical way to work this out.  


It's amazing I can't seem to find information on the Internet about this.  I wonder what audio shops do?"

Thanks in advance for your comments,

Louis


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My 12" Jelco overhang is meant to be 15mm but it's about 10mm with no discernable negative effect. The 750L comes with a template so not sure why this is even an issue other than the feeling that the bolts should be in center of slots.

Schubert, I have a fairly broad range of musical interests, chamber music, symphonic, mostly mainstream jazz (Coltrane, Monk, Miles, Bill Evans, etc; blues and some R'nR.

I love good music, as long as it's what I consider good. Not big on rap or opera (although I do listen to Wagner's Ring Cycle on pristine vinyl on occasion). I'm guessing you have an affinity for Schubert?

Regards,
Dan 
Yes, he led me towards classical music which has done more for me than anything else of human origin   in my life .
I'm a bit  ashamed I was so bold . when I  joined A'gon I thought there was nothing but R&R fans on here so I acted out .
Thanks for all of your responses everyone, my friend has figured it all out, happy and a healthy New Year to all you A'goners.  May we all have a great year.  Happy Listening!!!

Lou,  So are you going to tell us Jelco owner what the conclusion was, or are we gonna wonder if our arms are installed correctly?