[mike_p]

Hi all,

Anybody know where to find one?

Thanks much. Long days and pleasant nights.

Mike

[sturgus]

This might work.
http://www.ebay.com/itm/Jelco-SA-750D-SA-250-Armboard-Plate-Technics-SL-1200-1210-MK2-MK3-MK4-MK5-M5G-/160868179802?pt=Turntable_Parts_Accessories&hash=item25747d9f5a

[BPoletti]

It's a pretty standard mount.  If you can find a board for most any of the Jelco-sourced 9" arms, it should work.  Look for Linn, Sumiko, Audioquest armboards.  IIRC, they are all interchangable. 
My 750D was a drop in replacement for a Premeir FT-3.

[blakep]

My 750D was a drop in replacement for a Premeir FT-3.

While they're both technically "Linn mounts" in terms of diameter of holes, the 750D and FT-3 have very different effective lengths and requirements in terms of mounting distance. If you literally dropped your 750D into an FT-3 armboard your setup is seriously screwed up.

[BPoletti]

While they're both technically "Linn mounts" in terms of diameter of holes, the 750D and FT-3 have very different effective lengths and requirements in terms of mounting distance. If you literally dropped your 750D into an FT-3 armboard your setup is seriously screwed up.

Only if you use the stock geometry. 

[blakep]

What geometry would you suggest using to overcome the problem I've described?

[BPoletti]

Though there are many, the easy way is to just use what is recommended for the FT-3.  An arc is an arc.  It's just a matter of where the cart is mounted to create the same arc.  It's easy if you understand the basics. 

[neobop]

This might work.
http://www.ebay.com/itm/Jelco-SA-750D-SA-250-Armboard-Plate-Technics-SL-1200-1210-MK2-MK3-MK4-MK5-M5G-/160868179802?pt=Turntable_Parts_Accessories&hash=item25747d9f5a

This looks like a good one - 3mm aluminum.   You could call Kevin at KAB. I don't know if he has armboards for different arms.  An armboard has to fit the table, and be cut at the right distance, or very close.  You can't use an arc protractor on an arm mounted at a different distance.  In this case mounting distance is 214mm.  Mounting distance for an FT3 is close to 222mm.  8mm difference is not a good idea.  If you're buying an armboard (rather than making one) IMO you should get one like in the ad.  The price seems more than reasonable, and you'll save yourself a lot of grief, or buying another one.
neo

[blakep]

Though there are many, the easy way is to just use what is recommended for the FT-3.  An arc is an arc.  It's just a matter of where the cart is mounted to create the same arc.  It's easy if you understand the basics.

I understand the basics but I'm not sure that you do. As Neobop points out, an arc is not an arc when it comes to aligning a cartridge on two different arms with very different mounting distances and effective lengths.

The 750D has an effective length of 229 mm, the FT-3 an effective length of 239 mm so the arcs, using the recommended alignment/overhang by Jelco are very, very different. As Neobop also pointed out, 750D requires a mounting distance of 214 mm while the FT-3 is to be mounted at 221.7.   

If you mount the 750D at 221.7 you'll run out of room to align the cartridge properly in the headshell. It won't matter what alignment protocol you use.  It's as simple as that. I own both arms.

The 750D is NOT a straight drop in for the FT-3. Anyone who wants to try it is looking for a lot of grief. You can contact Jelco to confirm that.

The OP should seek out an armboard spec'd for the 750D (and the table it is to go on), which provides a mounting distance of 214 mm.

[BPoletti]

I understand the basics but I'm not sure that you do. As Neobop points out, an arc is not an arc when it comes to aligning a cartridge on two different arms with very different mounting distances and effective lengths.

The 750D has an effective length of 229 mm, the FT-3 an effective length of 239 mm so the arcs, using the recommended alignment/overhang by Jelco are very, very different. As Neobop also pointed out, 750D requires a mounting distance of 214 mm while the FT-3 is to be mounted at 221.7.   

If you mount the 750D at 221.7 you'll run out of room to align the cartridge properly in the headshell. It won't matter what alignment protocol you use.  It's as simple as that. I own both arms.

The 750D is NOT a straight drop in for the FT-3. Anyone who wants to try it is looking for a lot of grief. You can contact Jelco to confirm that.

The OP should seek out an armboard spec'd for the 750D (and the table it is to go on), which provides a mounting distance of 214 mm.

If you have direct experience with the two arms, please add that to your post so that we can directly comment. 

It is possible to properly align a cart mounted in a 750D using a FT-3 armboard.  I did it successfully with quite good results on both a Lyra Clavis da Capo and an AT OC9.  In the case of the CdC, I used a protractor supplied by the US importer.  I don't recall what I used for the OC9 as it was some time ago.  The CdC replaced the OC9 but it was probably the one supplied with the 750D.  There is quite a bit of room on the Jelco headshell for cart placement. 

[mike_p]

I'm the OP. I ended up going with an armboard fabricated by Sound Supports (a small UK firm). They use 2 pieces of aluminum of 3 m. Ea for the unit.

I got some feedback on Vinyl Engine that using an armboard with the Jelco spec'ed 214 mm arm mounting to spindle distance (with a Denon DL-103) will present alignment problems using Baerwald alignment, i.e., the cartridge won't be able to fit far enough back in the headshell to hit the null points.

Any thoughts on this?

[BPoletti]

I'm the OP. I ended up going with an armboard fabricated by Sound Supports (a small UK firm). They use 2 pieces of aluminum of 3 m. Ea for the unit.

I got some feedback on Vinyl Engine that using an armboard with the Jelco spec'ed 214 mm arm mounting to spindle distance (with a Denon DL-103) will present alignment problems using Baerwald alignment, i.e., the cartridge won't be able to fit far enough back in the headshell to hit the null points.

Any thoughts on this?

Depends on the cart.  I didn't have any trouble. 

[Wayner]

I'm the OP. I ended up going with an armboard fabricated by Sound Supports (a small UK firm). They use 2 pieces of aluminum of 3 m. Ea for the unit.

I got some feedback on Vinyl Engine that using an armboard with the Jelco spec'ed 214 mm arm mounting to spindle distance (with a Denon DL-103) will present alignment problems using Baerwald alignment, i.e., the cartridge won't be able to fit far enough back in the headshell to hit the null points.

Any thoughts on this?

Use the Lofren B alignment. At 214mm, you will need a 18.361 overhang, as opposed to a 17.894 for the Bearwald (
(Lofgren A). I believe that all Jelco arms are the same and are designed for a 210 mm pivot to spindle spacing.
You have boldly gone 4 mm beyond the recommended mounting, and as I would expect, have now encountered alignment
problems.

Wayner

[blakep]

If you have direct experience with the two arms, please add that to your post so that we can directly comment. 

It is possible to properly align a cart mounted in a 750D using a FT-3 armboard.  I did it successfully with quite good results on both a Lyra Clavis da Capo and an AT OC9.  In the case of the CdC, I used a protractor supplied by the US importer.  I don't recall what I used for the OC9 as it was some time ago.  The CdC replaced the OC9 but it was probably the one supplied with the 750D.  There is quite a bit of room on the Jelco headshell for cart placement.

As I said, I own both arms. I have a 750D mounted on a Gyrodec right now at 214 mm pivot to spindle and previously used an FT3 mounted at 221.3 on the same table with a different arm board. The FT3 is in storage. The arms require different armboards.

More power to you if you achieved alignment. I don't see how it's physically possible-if you mount the 750D at 221.3 and then tried to achieve the 17.3 mm overhang and 239 mm effective length of the FT3 and align to the FT3 arc with the 750D as you suggest-you'd need to move the cartridge almost 1.8 cm further ahead in the headshell and the 750D only has 1.5 cm of slot room in total on the headshell. You could reduce the overhang by 2-3 mm by going with a Stevenson alignment but that is still really pushing the limits, along with the fact that the offset angle will also be quite different and it certainly does not fit into the realm of suggesting that the 750D is a "drop in" replacement for the FT3.

[neobop]

The 214mm mounting distance is apparently right.  Overhang is 15mm so eff length = 229.   

I'm the OP. I ended up going with an armboard fabricated by Sound Supports (a small UK firm). They use 2 pieces of aluminum of 3 m. Ea for the unit.

I got some feedback on Vinyl Engine that using an armboard with the Jelco spec'ed 214 mm arm mounting to spindle distance (with a Denon DL-103) will present alignment problems using Baerwald alignment, i.e., the cartridge won't be able to fit far enough back in the headshell to hit the null points.

Any thoughts on this?

Factory null points are 59.1 and 112.5mm.  This might present a problem, but the person on VE must have misunderstood?  A Baerwald alignment would require a longer headshell, not shorter.  You've already ordered an armboard at specified distance.  Maybe you'll have enough room, as BPoletti suggests.  If the slots aren't long enough for desired alignment, I suggest an aftermarket headshell, one where the mounting screws can be further forward.  I'm not sure what's available these days, perhaps a vintage Orsonic.  Maybe you won't need it.  A Linn type arm has an eff length of 229, it mounts at 211.  While it seems that you're 3mm short in overhang adjust-ability, it really depends on the particular cart and position of headshell slots. If you can't get your preferred alignment, we'll help you find the right headshell or use an intermediate alignment.
neo

[blakep]

I'm the OP. I ended up going with an armboard fabricated by Sound Supports (a small UK firm). They use 2 pieces of aluminum of 3 m. Ea for the unit.

I got some feedback on Vinyl Engine that using an armboard with the Jelco spec'ed 214 mm arm mounting to spindle distance (with a Denon DL-103) will present alignment problems using Baerwald alignment, i.e., the cartridge won't be able to fit far enough back in the headshell to hit the null points.

Any thoughts on this?

OK. Let's clear everything up here. The 750D is supposed to mounted at 214 mm. so you have the right armboard. You will have absolutely no problem aligning to Baerwald. As neobop just said, you will be moving the cartridge ahead in the headshell to achieve Baerwald, not back, and you will have plenty of room. It's probably more difficult and a "tighter" fit aligning to Jelco's recommended protocol with a 15 mm overhang as you will be very jammed up at the back with the cartridge leads.  Bear in mind that when you do align to Baerwald on the 750D that the offset angle changes and the cartridge will NOT be square in the headshell but will be angled very slightly toward the spindle when you are correctly aligned.

I've attached a photo of my 103R (it is in an aluminum body but has the same overall dimensions as the stock 103/103R) aligned using Baerwald (17.894 mm overhang). I use a custom headshell on my 750D that actually has a bit less "slot" room than the stock Jelco headshell (that is one thing that BPolletti and I can agree on-it has a fair bit of room) and you can see that there are no difficulties. I would recommend that you use flexible headshell leads-the Jelco leads are quite good in this respect-something like the AT 6101's which are quite a bit stiffer could present troubles for you.