Mission (Original) 774 Tonearm I've had a long term hankering for a mission 774 Arm, the original as apposed to the later and inferior, 774SC and 774SM models. I've heard quite a few over the years, including a couple on Garrard decks and they always sounded good to me. I nearly bought one a decade ago, but spent to long thinking about it and lost out. More recently, I was offered a boxed item from a fellow forum member, so I made the purchase. For those of you that have been living under a rock for the past 40 years, this is what one looks like. The arm is capable of working with a wide range of cartridge compliances, due to its fluid damping, but fundamentally its a very low mass Arm at 5.5g, so Medium to High compliance cartridges will probably be best suited. There is no headshell as such, just a threaded alloy block on the end of the arm, overhang is set by adjusting the arm length. The threaded block, requires cartridges be mounted from below. Most of the Cartridges I've been considering for this arm are modern designs and have threaded bodies, which require screws be fitted from above. With great reluctance (Originality), I drilled the Alloy block, to create through holes. I can now mount virtually any cartridge on the arm. The Aluminium M2.5 fixing screws look tidy and will make mounting/adjustment easy, on a cartridge with a threaded body. Counter Weights The standard weight is made up of three parts, an inner metal tube that's threaded internally, with a thumb grip at one end. An outer metal sleeve which forms the mass of the weight and a flexible Sorbathane filler between the two, that acts as a damper. When attaching or adjusting the weight, it's important to use the thumb grip to rotate it. If you use the body of the weight, you risk tearing the Sorbothane away from its bonding to one of the metal parts, the cause of many sagging weights. There is also a simpler solid weight. This has a fairly thin metal end cap, with just a few threads, allowing it to be screwed onto the arm. Extra Weight Back in the day, there were a couple of extra weights available from Mission, to help when mounting heavy cartridges. These took the form of rings that slipped over the main weight and are held in position by a grub screw. By adjusting the rings position on the main weight, its effect could be varied. They are a rare find these days. Bias Setting To adjust the bias there's a sliding weight/s, these are the instructions from the manual. Fluid Damping The damping on the 774 comprises of a bent wire paddle fixed to the Arm, which dips into a trough of Silicon Oil, like so: Three different paddles came with the Arm and I've detailed them here: The Silicon Oil is available from Audio Suppliers, but at a premium price. It can also be obtained, at a lower price, from suppliers of parts for radio controlled model cars. They use it for shock absorbers, transmission gears, etc and its available in many viscosities. A grade of 30,000 cSt is a good starting point, or maybe the thicker 50,000 cST. The paddle used, the viscosity and the oil level in the trough, determines the amount of damping, so the figures for compliance above are just an approximate guide. Arm Base There were several Arm Bases used on the Original 774 Tonearm. This is the round base, which was fitted to the Mission 775 SM Turntable. Many of the arms fitted to this Turntable had the solid counter weight, without the Sorbothane damping. Probably to reduce costs, as it was a fairly low price Turntable. These are the two bases that most owners will encounter. The one at the top of the image is the early cast Aluminium base, it has a grub screw that pinches the arm post to hold its position. On these old arms, the hole for the arm post often wears and the grub screw just pushes the post against the far wall of the hole. This doesn't always hold the arm perpendicular to the base (Plinth top). So not my favorite design. The lower image is the later fabricated Aluminium base, it has a slightly deeper hole and a "C" clamp which grips around the arm post. This gives better support and is more likely to be perpendicular. While I prefer it to the early type, it's still not the last word in accuracy, it looks a bit industrial as well. Neither of these bases offers adjustment for the Pivot to Spindle distance. So it looks like I'll have to design and make my own arm base, one that allows the Pivot to Spindle distance, as well as the VTA, to be adjusted. I only have basic tools at my disposal, no Lathe or Milling machines, so I will have to think outside the box when designing it and maybe re purpose parts meant for a different role. I measured the arm post at 15.6mm diameter, what immediately sprang to mind was water pipes! In the UK, water/central heating pipes use 15mm Copper tube, so I searched to see if any of the common fittings would offer a solution and this is what I came up with. It's a 15mm Tank Outlet. 1/2" BSP external thread and a compression fitting. This has a 15.2mm dia bore to accept a 15mm tube. I can use an adjustable reamer and enlarge the bore, to create a good sliding fit with the arm, of approx 15.8mm dia. The locating nut looks industrial, but I can drill/tap my base and screw the fitting in from the underside.So this nut wont be used to hold the fitting, but it'll make a good spacer, to reduce the amount of thread protruding through the top face. The compression olive can be cut to form a "C" shape, which will allow it to fit over the slightly larger arm post diameter, it doesn't require a water tight seal so the cut is inconsequential. This cut will also stop the olive being compressed onto the arm post and sticking, which would prevent VTA adjustment, using a harder brass olive is preferable to the very soft copper variety. The olive locates into cone shaped recess's in both halves, which have the effect of self centering the Arm. The compression nut also looks a bit industrial, but I have a few of the old Conex nuts, which are better for finger adjustment and as can be seen below, look much nicer. I'll clean one of these up and remove the lettering. The drawing above is what I have in mind, the stock base plates both use the SME bolt pattern. My bolt locations, when in the middle of the adjustment slots, duplicates these SME dimensions. I'll fit threaded inserts into my plinth to match, giving 220mm Pivot to Spindle distance in this central location. So my adjustment range for Pivot to Spindle distance will be 210 to 230mm. I had some 10mm thick Aluminium plate off an old Amp front, which I cut, very approximately, to the size of the base. Then drilled the arm location with a 19mm bit and tapped it with a 1/2" BSP thread. This was a quick attempt to see if it pulled up perpendicular to the plate, which it did. I can now unscrew the fitting and continue making the plate around this threaded hole. I've been experimenting with some ruled stick on plastic tape, to help when setting VTA, this also seems to work well. Trial fit of the arm base plate. The completed Base Plate. The arm needs a rewire, which I will do prior to fitting to my deck. I'll keep the stock Base and Harness safe, for originality purposes. Offset Angle There is some debate as to what the angle of the cartridge mounting block is, or should be, with some claiming that it was changed during the production life. I can't say with any authority if this was the case, or whether it was just production variation. Figures ranging from 20.5 deg to 22.5 deg have been talked about, I can't imagine that such a well designed and made arm would have such a large discrepancy though. On the other hand, how accurately are people measuring the offset? To satisfy myself that I could align a cartridge correctly, I made a template to measure my particular arms offset angle. This template can be found in the thumbnails, as a link to a PDF file. By printing this at full size, it can be used to measure the angle. Range is from 20 to 23 deg in 1 deg increments. It will be easy to establish 0.5 deg steps between these settings. Any smaller increments are not worth considering, as there will be enough play on the cartridge fixings to cater for this amount. Pivot to Spindle Distance (Mounting distance). There is also some confusion as to what this should be and Mission themselves are the cause of this. The Manual shows a diagram with a dimension of 215.4mm and this is what most people use. But there is also a Mission badged Arm mounting template for the "774" that has a dimension of 8 . 9/16"  which equals 217.5mm. Do you believe the manual, that may have been proof read by non technical people, or the mounting template, where its sole purpose is to acurately position the Arm? Or was this template meant for one of the later 774 variants? According to the database at vinylengine the 774SC and 774SM had a pivot to spindle distance of 210mm, so that doesn't tie in with either dimension. It's a Mess! The only dimension that Mission quoted in the manuals specification page, was the Effective Length of 229mm. Without an accurate Pivot to Spindle distance and Offset Angle you can't set the cartridge correctly, I'm surprised people get such great results with the arm. Maybe the 215.4mm is correct? These are the most widely adopted figures for this presumed "Mission" Alignment : Pivot to Spindle 215.4mm Effective Length 229mm Offset Angle 20.5 deg If you put these through the Vinyl Engine alignment program, it plots some pretty poor results, in terms of tracking error and distortion, compared with the usual bunch of alignments from Lofgren A (Baerwald), Lofgren B, or Stevenson. This leads me to another point, so many people these days, strive to achieve Baerwald alignment, even twisting their cartridges on various arms/headshells, to achieve the correct offset angle. This is probably due to Baerwald having the lowest maximum error/distortion. But surely there is more to it than this one aspect. I ask myself, why did so many Arm manufacturers use their own alignment and why was this close to Stevenson for their 9" Arms. Companies like: Technics Dynavector Grace Jelco Audio Technica Rega All the above, used Alignments close to Stevenson. Here is a comparison of Technics/Rega/Audio Technica/Stevenson alignments: The manufacturers seem to know something the rest of us don't, as they all go for similar error and distortion curves. Again, these figures make the Mission alignment look poor. I'm not disputing that the 774 is a great Arm, I've heard it produce fabulous results. I'm just questioning the validity of the alignment dimensions being quoted around the Internet and wondering if it could be tuned for better performance. I don't have any faith in the figures available. Mounting the arm I set the arm up on my Lenco based deck, using the stock, presumed Mission values, that I listed above. This was the result. As you can see, with the 229mm effective length, the point where the cable exits the side of the wand is under the clamp and it traps/crushes the wires in this position. My wand is a genuine Mission double wall item, with the Mission badge on the front of the mounting block. I'm confident it's the one that came with the Arm, as copies tend to be single wall and don't have the badge. There is something seriously wrong here. I eventually found the cause of this problem, see these two pictures taken from an early arm manual (bottom) and a later arm above. If you compare the two, the wires exit much closer to the end of the wand on the lower (earlier) version. Approximately 19mm compared with 30mm. This, coupled with the wider clamp on the later body, was what caused the issue. What I in fact had, was an early base plate and wand, with a later body, containing the larger trough and clamp. My own Geometry Not being totally happy with the distortion characteristics of the original geometry anyway, I decided to create my own, using the program on the Vinyl Engine site and got the following results. I've listed the so called Mission values, stock Lofgren A (Baerwald) and Stevenson for comparison. I used the 229mm effective length for these, note the offset angles are not achievable due to the fixed mounting angle on this arm. My wands mounting block has an offset angle measuring 21deg. My alignment is traced in Blue and sits midway between the "Mission" and Stevenson alignment for tracking error and distortion. Not as good as Stevenson on the first couple of tracks on an album, but better from there till the end. The Mission geometry plots as though it were designed for singles only, very low tracking error and distortion over this range at the expense of the first half of an album, the first track being particularly poor. I re-wired the Arm with Missing Link (Silver platted Copper) wires. With my geometry, the tonearm wires now exit the wand just in front of the clamp, so its a win, win situation for me. This geometry increases the effective length and will also work if you have the correct combination of parts on the later version of the arm. But my geometry wont work on the correct early version (narrow clamp and exit hole 19mm from wand end), as there will not be sufficient wand in the clamp to grip it effectively, if at all. To re cap, my alignment is: Spindle to Pivot = 225mm Effective Length = 239.5mm Offset Angle = 21 deg This seems a lot better, my wand sits in what looks to be the correct position in the clamp, the cartridge sits square in the mounting block and as mentioned, it shows better tracking/distortion characteristics on the Vinyl Engine alignment program. My alignment protractor, to achieve this set up, can be found linked in the thumb nails. The downside of this alignment, is that the mounting distance of the arm needs to be increased by 9.6mm, this was not an issue for me, as my new arm base could cater for the adjustment. A stock base, having no adjustment, would have to be re-mounted to the new dimension. So how does it sound with this alignment? I loaded it with a Van Den Hul ONE Special, the cartridge lined up perfectly with my protractor and sits exactly square in the mounting block, which indicates my measured 21deg for the Blocks offset angle was correct. It sounds fabulous, very low surface noise and a Black background would tend to suggest my alignment is a good match for the arm. Loving this combination of Arm/cartridge on my modified Lenco L75 turntable. Its certainly living up to its reputation as a very fine arm and I look forward to many years of listening pleasure.