Drilling a hole for tonearm

[AJSki2fly]

I thought it was agreed it's 214 pivot to spindle, effective length is pivot to stylus. When you say vertical position, do you mean with the plinth standing on the front edge like a vertical turntable that would probably be linear tracking. I usually use a pencil to draw an arc at the pivot to spindle distance then decide where the arm works best, for example to check the tail end of the arm doesn't foul on anything like a cover and check the headshell doesn't foul on the controls.

Yep I agree its odd that Jelco mark the setup protractor as 229(effective length) but pivot to spindle is 214, very confusing, but Mike has checked and 214 is the measurement. Yes I agree actually drawing an arc and then deciding the best position is the sensible solution, I was making the silly assumption that you would want the arm parked parallel to the edge the plinth, hence have the arm lift facing the front edge of the plinth.

[Mikeandvan]

IMG_20191205_205448337_HDR by Mike Van, on Flickr

Seems slightly above the corner is the only way to get the right pivot to spindle distance, any lower and the armboard touches the 401 unit, is it ok in this position? Would it make a difference if it was lower in terms of the angle that the stylus hits the record.

[AJSki2fly]

IMG_20191205_205448337_HDR by Mike Van, on Flickr

Seems slightly above the corner is the only way to get the right pivot to spindle distance, any lower and the armboard touches the 401 unit, is it ok in this position? Would it make a difference if it was lower in terms of the angle that the stylus hits the record.

The key thing is that the distance from the centre of the spindle to the centre of the arm pivot point is 214mm, which as you have already said is the distance you have at the 255 mark on the template(confusing as it is). The angle as you put it(lateral angle I think it is) that the stylus hits the record will be the same for any position the pivot arm is at 214mm from the centre of the spindle. This is assuming that having set up the arm on the plinth you then set up the position in the head shell correctly using a stylus alignment protractor https://www.vinylengine.com/cartridg...tractors.shtml

[scotty38]

As Adrian has said, as long as it's placed on the arc scribed by the point actually 214mm from the spindle you'll be fine. Aesthetics are another thing though and I think where you have it in that corner will probably look best.

Having said that why not post pictures, side by side, of where it is now and clockwise just past the top right corner and we can see what would look best?

[awkwardbydesign]

Yep not sure where spindle pivot of 229 keeps coming from

229mm is the effective length. It means there will be a 15mm overhang. Stylus (229mm) 15mm beyond pivot (214mm). Normal, but variable, depending on arm geometry.

[scotty38]

229mm is the effective length. It means there will be a 15mm overhang. Stylus (229mm) 15mm beyond pivot (214mm). Normal, but variable, depending on arm geometry.

Thanks but I'm well aware of that. I didn't want anyone drilling a hole 229mm away from the spindle.

[paulf-2007]

That gauge could easily confuse, better to get a piece of thin wood or ruler, drill two holes 214mm apart, one hole over the spindle and a pencil in the other, scribe an arc job done. That picture of the gauge at 229 shows the tone arm will not go on the corner, either behind or at the side if there is room

[Barry]

The Jelco 750D arm has an effective length (stylus to pivot) of 229mm, with an overhang of 15mm. Thus the TT spigot to arm pivot distance is 214mm (229 - 15 = 214mm). The installation protractor is marked with the effective length of the arm you are wanting to install, hence in your case '229'.

The null radii (on the alignement protractor) will be 59.1mm and 112.5mm.

Where you drill the hole for the pickup arm won't matter, as long as the distance from the TT spigot is 214mm. Choose anywhere on the arc that doesn't cause the counterweight end of the arm to foul the lid of the plinth, but is not too far in a clockwise sense that makes the pickup difficult to cue.

[Mikeandvan]

Thanks to all replies, the mounting collar is just slightly above the corner of the 401 motor unit, will fit tonearm tomorrow, dunno what it will sound like! I'm expecting to be crap for some reason? Saying that I do have a AG1500 mains regenerator which I've heard can help the 401 motor somewhat. ALso the sme plinth has been lead lined, what I don't get is how many 'posh' 401 plinths have the tonearm connected to the same plinth as the motor unit, surely the vibrations will affect performance? I also won't have much room for a fancy plinth once I get around to buying a proper one, so armboard will need to be close to the motor unit, as it is now.

[Mikeandvan]

Anyone know what size holes to drill for the 3 mounting screws for the Amnonite Jelco collar? Will need to use screws rather than the alan bolts provided as I don't have a tool to make threads.