mission 774 tonearm restoration

[Ant]

I got this arm off Steve at the last Owston and have finally got my act together to make a start on it.
I've got myself some wiring and some other bits and bobs, the replacement arm wand connector is off xad on ebay who seem to have most of the small parts required to rebuild one.

Mission 774 tonearm restoration by anthony cresswell, on Flickr

The internal wiring is Cardas, the external wiring is Van Damm classic xke as it has a very low quoted capacitance per metre of 55pf. Cart tags off Malvern audio, Neutrik phono plugs from compass audio as I pretty much only use Neutrik for plugs and sockets now because they just work and fit properly. and aren't silly expensive. And the connector bits as mentioned off xad.

I also have some carbon fibre tube from Steve to make another arm wand, thought i'd fix the original one first. First issue with the original wand is that the tapped holes are no longer tapped, someone must have cross threaded them at some point. so we will fix that first.

Mission 774 tonearm restoration by anthony cresswell, on Flickr

The mounting block is slightly bigger than the tube diameter as you would expect, so I dialled it in along the tube length with a finger gauge and shimmed it so the holes are redrilled square to the block

Mission 774 tonearm restoration by anthony cresswell, on Flickr

drilled the through hole out to 2.7mm to allow the use of Japanese spec 2.6mm bolts, probably the reason the threads got ruined in the first place.
Used Perspex offcuts under the wand to allow drilling through, I like to use perspex for this because it is very flat and a very consistent thickness across its length, so when you machine things in the mill you know stuff is still square to the table. No need to re paint it either, the holes came through very cleanly

Mission 774 tonearm restoration by anthony cresswell, on Flickr

[Ant]

Next thing to do was to wire the wand. But the Cardas internal loom doesn't have an earth wire in it so we will hang fire on that for now.
So, the connector arrangement was fitted to the baseplate so the external wiring could be done. Took the time to scribe between the tracks on the matrix board to make sure there were no potential shorts before and after soldering it all up

Mission 774 tonearm restoration by anthony cresswell, on Flickr

The pins were soldered on and the wiring soldered to the matrix board

Mission 774 tonearm restoration by anthony cresswell, on Flickr

So, that section is done, although the little set of diagrams that came with the connector shows to secure the external wiring to the arm post as strain relief. Seems like a daft idea to me, how are you supposed to set the arm height if the wiring is zip tied to it? I'll come up with a different solution.

Next job will be the wand wiring. This one is a little headscratching, I'm not sure whether the 774 really needs a wand earth for a start. My unipivot doesn't hum and there is no internal arm earth on that, only arm I've ever had a hum problem with is an rb250. I'm not sure how it was wired originally because there was no loom in it, but the new connector block and pins does have provision for a fifth pin to be wired for an earth lead

So, any comments? I'd rather not have to pull the loom out once its in in order to add an earth. Perhaps I should just see if I can get an individual strand of wire and just do it

onwards!

[shane]

Watching with interest as I did the same a while ago. I counter-bored the cartridge mounting holes so the screw heads sit flush with the top of the cartridge mounting block. Looks neater and means you can use shorter bolts.

Since the plug and socket from xad are 5-way rather than 4-way I was also able to wire it fully balanced to my step/up tx. If you carefully prize the Mission badge of the front of the block you’ll find an earth wire attached behind it.

[Ant]

It's missing the mission badge anyway Shane, I'll have to make a little cover plate up for it. I presume you mean the little pin that sticks up? It looks like the block is a resistance fit and is then pinned in place with it. The wand earth is then soldered to that then?

[shane]

The wand earth is then soldered to that then?

Yes. I ran a lead from there back to the plug, then took that to the lead screens. I used twin core screened on each channel to a 5-pin DIN plug on the step-ups.

[Ant]

Ok cool, ill order a spool of litz wire and run a length from there to pin 5 then run a wire from there for the ground terminal

[Ali Tait]

Ant, the head holes were often drilled out on these so carts with threaded holes could be fitted, I did so on mine.

[Ant]

Got more work done on the arm over the last week.

Slow progress because I ended up in A&E last Tuesday after I went mostly blind in the left eye apart from the centre and about half an hour later my left hand went numb. Vision came back after about half an hour, then the hand went numb. The doctor in A&E thought I might have had a mini stroke, told me to take a hefty aspirin dose and take it easy and to wait to be called for an appointment to go and see a consultant.
Saw the consultant on friday who thinks that it was most likely an occular migraine, but didn't completely rule out a mini stroke because of the numb hand.
That properly shit me up...

So, while sat on my arse I got more done.
wired the arm tube, see the little wire hook for pulling the wiring through the holes in the arm tube
Mission 774 tonearm rebuild by anthony cresswell, on Flickr

The earth for the arm tube is some copper litz, and was wired as per Shanes instructions to the pin securing the cart mount block.

The wiring was then soldered up to the connector block while it was held in one of my small vices

Mission 774 tonearm rebuild by anthony cresswell, on Flickr

The wiring was done according to xad instructions and loop length

Mission 774 tonearm rebuild by anthony cresswell, on Flickr

Next job was to fit it to a deck. I thought it would go straight on the technics sl150 because the original arm board was for an SME 3009, however the mission baseplate is not exactly the same size as the SME one and the mounting holes were not the same either, so I had to make one.
Ordered a couple of 120mm matt black perspex discs and knocked up a baseplate for the mission. Also had to buy some replacement feet for the Technics, the ones that were on it are missing in action. no idea where they are or what they were taken off for...
While doing this I found that there is some conflicting information out there about the mounting distance for the arm. There appears to be no real consensus, a lot of people on forums and such state that it is supposed to be 214.5mm spindle to pivot distance, but missions own template shows a distance of 8 9/16" which translates to 217.48mm. So I used that and it seems to be lining up well enough. I haven't set it up perfectly, it wants some fenagling when I get some more time.

Mission 774 tonearm restoration by anthony cresswell, on Flickr

All works fine, I initially tried the Goldring 2300 on it but it didn't seem to like the Goldring, so I dug out the Empire 1000gt. That cart tracks at 1.25g and is high compliance and seems to works better in it.

Mission 774 tonearm restoration by anthony cresswell, on Flickr

Next jobs are to make some replacement paddles for it for the damping trough, and to sort out the arm lift bar as it doesn't quite fit properly so it rocks about when the arm is lifted. Initial impressions with the empire in it are that it seems to not make itself known, it does a disappearing act. Perhaps the 2300 will get on better with it with some damping

Onwards!

[shane]

Interesting stuff! Not sure you need the mass ring on the counterweight with a cart like the Empire.

[Ant]

Cant get it off, the setscrew wont move. Ill need to do a bit of faffing to get it out.
Could put the other solid counterweight on it to see what the difference is

[Ali Tait]

Damping will definitely help, not found a cart that won’t work well if you get the damping right. Really good arms these imo.

Hope you’re doing ok Ant, and it was a migraine. I get the occular ones occasionally, get squiggly lines with what looks like a turning kaleidoscope inside, and I lose vision where they manifest. Always around the periphery, never in central vision. Not had any numbness, though sometimes feel a bit squiffy. Usually last 15-20 mins and I only get them when I’m very tired. No headaches though thankfully.

[Ant]

Did some proper setup with it today. I cant find the original null points so tried baerwald first, that was a no go, i cant get it to line up at both points in a way i would find reasonable.
Next tried stevenson, thats much more like it. It will do the inner 60.325 null bang on and the outer 117.4 null is very close. Not perfect, but move the null to give or take 115 and it lines up bang on so ill take that.

I know the empire cart sound well, it was on the jvc for a good while and used practically every day, in the mission i can detect a little tiny bit of midrange bloom on level 42 persuit of accidents, (my go to lp because i know it so well) that isnt there with the jvc.
The jvc robot arm is also q damped albeit not fluid damped but by the electronics in the arm so its probably that. Be interesting to see what the fluid damping does when i get some paddles made. As it is without the paddles, its simply a low mass arm with a high ish compliance cart in it. Which is fine.
Otherwise, the arm seems to behave nicely and not really sound of anything.
The technics is not behaving however. The technics that had supposedly had every cap replaced on the board. That hadn't had anything at all replaced when i looked inside..
Well its decided its only going to start when it feels like it and lose its pitch stability on a whim.
So that wants fixing now.
Why am i not surprised, i have had no luck ever with any technics deck ive had.

[Neal]

Hope you’re doing ok Ant, and it was a migraine. I get the occular ones occasionally, get squiggly lines with what looks like a turning kaleidoscope inside, and I lose vision where they manifest. Always around the periphery, never in central vision. Not had any numbness, though sometimes feel a bit squiffy. Usually last 15-20 mins and I only get them when I’m very tired. No headaches though thankfully.

Wow, snap Ali, i’ve always wondered what it was. Bright lights and too much caffeine trigger mine.

Hope you are ok Ant, my old SL150 used to wander about pitch wise as well, the speed adjustment pots go bad after so many years

[Ali Tait]

Fairly common I think Neal, it only happens a few times a year for me thankfully.

[Cressy Snr]

Yep, happens with me too occasionally. I have had numbness with it like our Ant, but on one side of my head rather than in the hand.