Author Topic: Doc Viljoen/SABC Mark 3 turntable #288 restoration  (Read 1646 times)

Offline IvMan

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #30 on: October 11, 2017, 11:05:16 AM »
Ok, wont do then.
The achromat is only around 12"

Offline Schalk

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #31 on: October 12, 2017, 10:48:16 AM »
I could have an Alu, copper or brass one laser cut for you with my next laser cutting order. That will see you only pay for the item and not the minimum cutting charge which is about 600 odd. If out of Alu, would probably cost you 150 to 200 max I guestimate. Copper or brass obviously might be almost at the minimum charge. One should have the spindle hole "just undercut" and then ream to exact fit to prevent out of centre/excentric issues. The outer edge should be finished before reaming the spindle hole by supporting with an exact fit mandrel in the undersize spindle hole, fitted to a jig which could be attached to your bench drill platform. Then turning it evenly against a sanding drum running in the drill at medium speed. Note that it should JUST be touching the drum (fine grit) and entered with rotation in the OPPOSITE direction to what the drum is spinning, this should prevent the drum ripping it out of your hands and cutting all your fingers (the disc of course).  Like Skollie says check against gripping and spinning it right through your chest  :help: Final polish and then ream the centre hole to size.

If you do not have a bench drill, I could do the above bit for you, leaving you only the spindle hole to finally ream for the perfect fit...

Like I said I could order this with my next order at cutting and material cost to you, my order covers the minimum cutting charge. My pleasure to help get this heirloom up as it should be.

Your call :2thumbs:

Offline JohnnyIC

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #32 on: October 12, 2017, 01:59:10 PM »
I could have an Alu, copper or brass one laser cut for you with my next laser cutting order.

Wow thanks for the offer. I was considering having the top platter laser cut but the one place in Bloem who does laser cutting refuses to cut aluminium for fear of damaging his laser. I will just have to get the exact diameter and thickness and get back to you with this, the thickness probably isn't too crucial though. Please let me know via PM when your next order will be going out.

Offline Schalk

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #33 on: October 12, 2017, 03:57:29 PM »
Shall do so squire  :thumbs:

Offline mygoggie

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #34 on: October 12, 2017, 05:28:42 PM »
I could have an Alu, copper or brass one laser cut for you with my next laser cutting order.
I am coming late into the project but you need to stick to same metal on same metal with the platter and plate. If not you are building an electrical cell and will have galvanic corrosion ...

Cleaning and polishing of your metal parts is very easy. Just soda blast them with a small blaster and from there polish using a slow speed polishing wheel with different grades of polish.

On the tonearm. You need to replace all the bearings in it. I have managed to source such at Bearing International. To remove them, heat the housing with a hot air gun FORM A DISTANCE and when the alu has expanded enough simply pull them out.Here is a thread on P77 restoration.

Rubber tyres - Soak them in glycerin to restore their flexibility. Make sure you squeeze dry them.

36V lights - Buy a simple 36VDC to 12VDC voltage converter and install 12V bulbs for the original effect.

Great project! Have fun  :2thumbs:

Offline Steerpike

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #35 on: October 12, 2017, 11:27:48 PM »
you need to stick to same metal on same metal with the platter and plate. If not you are building an electrical cell and will have galvanic corrosion ...

???
What about every other article in daily use that has dissimilar metals in contact?

Quote
36V lights - Buy a simple 36VDC to 12VDC voltage converter and install 12V bulbs for the original effect.

Not so simple as that.
The drive circuit will not cope with the higher current demanded by a 12V bulb. It needs to be buffered.
The vast majority of available 12V bulbs are of too high a wattage, they will burn the plastc mounting. They need to be run at about 8V. Unless you can find a really low current 12 bulb, I could not. LEDs look horrible in the pushbuttons.
« Last Edit: October 12, 2017, 11:31:14 PM by Steerpike »

Offline 1200GXman

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #36 on: October 13, 2017, 07:06:54 AM »
Unfortunately he is right. Especially with Aluminium. It creates something like "white rust".
Sansui AU-101, Sansui AU3900, Rotel RA935BX, Pioneer SA-6500 Mkii, Marantz PM53, DIY kit amplifier

Offline 2wice

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #37 on: October 13, 2017, 07:52:16 AM »
The 2 metals will be fine. Needs an electrolyte to work and takes very long. Can be ignored here.
Trenton Carr
Montana Park
Pretoria

Offline JohnnyIC

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #38 on: October 13, 2017, 08:19:49 AM »
As far as I'm aware there wont be any "metal on metal" contact between the top and bottom platter because of thin strips of cork/rubber between them? Steerspike or Agaton Sax can just confirm?

Offline mygoggie

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #39 on: October 13, 2017, 04:35:16 PM »
???
What about every other article in daily use that has dissimilar metals in contact?

With respect, I work with this everyday of my life. Just add an electrolyte, such as smog, salt air and off you go ... direct contact is not required. Air at 60% moisture content with smog carbon or salt from ocean air is more than enough for a galvanic reaction. Keep the alu on each disk the same material specs and you will be fine and ensure they make electrical contact with each other otherwise you will built a Van der Graaff generator....
« Last Edit: October 13, 2017, 04:43:25 PM by mygoggie »

Offline mygoggie

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #40 on: October 13, 2017, 04:38:04 PM »
The drive circuit will not cope with the higher current demanded by a 12V bulb.

Valid point, so first step would be to check the wattage of the existing bulbs. Post that value as well as the type and size of the bulb receptacle here and we take it from there.
« Last Edit: October 13, 2017, 04:41:39 PM by mygoggie »

Offline JohnnyIC

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #41 on: October 13, 2017, 04:52:59 PM »
Valid point, so first step would be to check the wattage of the existing bulbs. Post that value as well as the type and size of the bulb receptacle here and we take it from there.

On mine the original bulbs were replaced with LED's by the previous owner so I'll just leave it as is for now, can't really remove the LED's because they were glued in place.   :sulky:

Offline Agaton Sax

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #42 on: October 13, 2017, 05:12:41 PM »
Before silly arguments blow up into the second Korean War,here is the disc:

Subplatter separated from platter by stock cork(?) pads

IMG_0346 by jdza, on Flickr

Here with an Acromat fitted instead of the little plastic pimples that normally carries the record . Acromat is 12 inch.

IMG_0347 by jdza, on Flickr


Offline JohnnyIC

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #43 on: October 13, 2017, 06:04:12 PM »
Thanks for those pics, I was wondering if the cork strips/pads should extend all the way to the edge.

Offline 2wice

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Re: Doc Viljoen/SABC Mark 3 turntable #288 restoration
« Reply #44 on: October 13, 2017, 07:13:55 PM »
Air at 60% moisture content with smog carbon or salt from ocean air is more than enough for a galvanic reaction

With all due respect, if he has these conditions in his listening room, then he is Aquaman. /s
Trenton Carr
Montana Park
Pretoria