Lenco L75 based Turntable Project

[Qwin]

It looks very nice. Always good to get a plumbing fitting into a build too ;->

I have two Mission 774 arms, an early type (purchased Dec 79) and a later type. AFAIR (I can't find the earlier one ATM) they both have the same headshell offset.

The later one (which I have mounted on a Thorens TD124 II with a Decca SC4E) has the arm wiring exiting the tube around 30mm from the end and it's aligned so that there is about 8mm of arm tube protruding behind the clamp. The original template says the spindle to mounting position is 8 9/16" (217.5mm) and the original alignment protractor has the null point at 61mm. I can't recall what I set mine up to, but it sounds OK to me.

Yeh, that's different to my wand, exit hole for wires is less than 20mm on mine, this is why my wires end up under the clamp with stock eff Lgth, my clamp is also the wider type (they altered it).
You are confirming what I already thought.
The template might say 217.5 but the diagram in the manual says 215.4, its a mess.
215.4/217.5 the wires are still under the clamp on mine. I increased eff lgth nearly 10mm to clear the clamp.
So many undocumented changes on many of these old arms, not just Mission.
For the parts I have, my geometry seems to work very well, but I am well aware it may not suit all variants.

Yes, I like to plumb it in! The arm stub is 15.6mm dia, water fittings are 15.2mm dia to take a 15mm tube. I used an adjustable reamer to enlarge the fitting, till it was a sliding fit on the arm stub.

[Patrick Dixon]

my clamp is also the wider type (they altered it).

Yes, my early 1979 one has the shorter clamp. The earlier one is slightly trickier to set up with the damping trough from what I remember (I think the trough is slightly shorter too) - from memory I think the paddle can hit the end before end of side if you don't get it quite right, and you might need to have the arm at rest slightly not perpendicular to the plinth front edge to achieve that.

I have found my other arm wand now and it's the same length but has the wire exit about 19mm from the tube end (as yours is). This is the 1979 arm which I bought from the original owner. The manual for that arm has a correction stuck over the contents page and over the paddles section on the third page, and it also has the 8.48" / 215.4mm dimension on the diagram on page 2. The manual for the later arm has the pages reprinted with the corrections, and no 215.4 dimension on the diagram (there is a separate template). So I think you have a later base and pivot section and an earlier manual and wand.

(You can actually see the different trough casting shapes in the manuals - and maybe the clamp position is slightly further back?).



But anyway, you seem to have an effective and theoretically sound solution and a very nice looking deck, so I'm sure you are not going to loose any sleep over it! But it would be nice to get to the bottom of what Mission intended.


Mission 774 Manual Small.jpg

[Qwin]

Yes, I agree, if not for our sake, more for anyone purchasing one from scratch, not knowing any of these anomalies.

[karma1967]

more confusion as the manual states 215.4 spindle to pivot.
great work though ken!

[Patrick Dixon]

more confusion as the manual states 215.4 spindle to pivot.

It depends which version of the manual ... the later one doesn't.

Having played around with the calculator, I think the 229mm effective length is wrong (or they mean something other than spindle to pivot + overhang). The 'Mission Alignment Protractor' I have has the null point at 61mm so for a 20.5deg offset (if that's what it is) and 217.5mm pivot to spindle (as per the 'Mission 774 Installation Template' I also have) that would give an overhang of 13.75mm. I think this is what you'd end up with if you set the arm up using their templates (it may even be how mine is set!).

It will give you 229mm if you set spindle to pivot 215.4mm and null point at 61mm (overhang 13.6mm)

[Ali Tait]

I read somewhere to fill the silicone so that it just touches the bottom of the paddle you’re using. YMMV of course, they stated it would kill the sound if it was filled up. I have mine like this.

[drSM]

Ken has given every facet of the build his attention to perfection.
I ve had a front row seat, almost, with Ken's build.
I hope he wont mind me hijacking this thread.
In fact i did a parallel build here in KL Malaysia after i relieved my cousin of her late father's L75 telling her it was far too much trouble to sort out.
My search for suitable bamboo failed. But recycled ply from crate for Finnish mini CT scanner has done it for me.
I used 12 layers to make an 11 cm thick plinth.
Ken got me in touch with Sien who lives in the same city.
For this build I used his plates (so mine is not a PTP), main bearing and an asymmetric mount for arm base (to get S2P spot on).
Jelco 850S. and i ve been using a Denon 103R and Ortofon MC15 Super II both restylied .
I have a 5mm acrylic mat and O rings like Ken's to dampen the platter, but i decided against Sien's Cu mat
My motor was serviced by Sien but its still quite noisy, and there s a clicky sound that Lencoheads here conclude is from the idler.
Oddly very little of that is transmitted to the speakers .
This tt produces a very engaging sound with plenty PRAT1.jpg2.jpg3.jpg4.jpg
Feet are from Michael Lim of Rega upgrade fame(also a local chap)
Really pleased with this Malaysian L75 rebuild.
I ve secured another motor and will look into a new idler and that should do it.
Thanks Ken for all help.

[Qwin]

I read somewhere to fill the silicone so that it just touches the bottom of the paddle you’re using. YMMV of course, they stated it would kill the sound if it was filled up. I have mine like this.

I think it depends on the paddle size and viscosity used Ali.

Yesterday, I tried the med paddle and 30k cSt fluid, with the trough half full and it made very little difference, to being run dry.
Maybe the slightest improvement to the crispness (leading/trailing edges) of vocals.

[Qwin]

It depends which version of the manual ... the later one doesn't.

Having played around with the calculator, I think the 229mm effective length is wrong (or they mean something other than spindle to pivot + overhang). The 'Mission Alignment Protractor' I have has the null point at 61mm so for a 20.5deg offset (if that's what it is) and 217.5mm pivot to spindle (as per the 'Mission 774 Installation Template' I also have) that would give an overhang of 13.75mm. I think this is what you'd end up with if you set the arm up using their templates (it may even be how mine is set!).

It will give you 229mm if you set spindle to pivot 215.4mm and null point at 61mm (overhang 13.6mm)

I think your conclusions mirror mine Patrick, I had serious doubts about the geometry being proposed as the correct Mission values.
This was mainly because it plotted fairly poor results on the Vinyl Engine program and others. If you check the chart values and plots in my opening post, you will see my own geometry compares very favourably against the supposed Mission. Mission in Orange mine in Blue in the Plots. The distortion and error values are much lower for mine.

[walpurgis]

The usual improvements heard with fluid damping are in the bass, which may sound tighter and more weighty. This can be more evident with Deccas and low compliance MCs.