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Restoring and Improving A Thorens TD-124 MKII
Restoring and Improving A Thorens TD-124 MKII
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Old 7th December 2017, 02:45 PM   #2521
nigel pearson is offline nigel pearson  United Kingdom
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Their are two main types of resonance. The additive and subtractive, both are not really what one wants. Rubber subtracts. It's like a reactive electronic circuit. OSB has many followers as it has both the qulities of ply and some of MDF. To have resonance one makes all particles the same ( think many ball bearings in a frame ). To avoid it different is best. Cork in neoprene for mats seems to be an ideal compromise. OSB and MDF with perhaps animal glues could be good. Mass also is important. Too much can be a problem. 50 tons might work. I doubt 200 lbs is helpful. 20 to 60 lbs inc TD124 is about right. I use squash balls to suspend the motor unit and keep that mass as low as I can whilst being ridged. 25mm MDF and 6 mm ply bonded is OK for that. If you want concrete put it below the squash balls. BTW, they do go flat, they still work. Just shim them. In time they settle.
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Old 7th December 2017, 06:10 PM   #2522
kleppermaster is offline kleppermaster
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Quote:
Originally Posted by AndrewT View Post
Would it help start up and warm up to use a higher voltage, then reduce voltage to the fully warmed up after 20 minutes?

This could easily be done with an auto transformer.
125Vac to start up, 123Vac to warm up and 110Vac to 118Vac to run at chosen speed.
Update: 12/7/2017

OK, today I tore the table down and re-lubed the motor bearings, idler wheel and stepped speed pulley with 3-in-1 electric motor oil.

Here are the results:

The table spins up to speed just fine. That problem is solved.

However at line voltage (120VAC) with the eddie current magnet adjusted as close as it can be the table runs way fast out of adjustment range.

I tried adjusting the voltage using my cool little switched transformer. First I tried 118VAC. Slower, but still fast out of adjustment range.

I kept stepping the voltage down to 104VAC. Each lower step led to slower speed, but even at 104VAC, the table is still a bit too fast.

Below 104VAC the strobe light would not light.

My suspicion is that my eddie current magnet is weak. Is there a way to re-magnatize it. Does anyone offer this service?

Other potential solutions:

Eddie current solution, Place adhesive backed magnetic tape on the vanes inside the stepped pulley.

Eddie current solution, Place neodymium magnets on the existing magnet to boost it's strength.

Voltage solution, I looked at the circuit that is used to switch the input voltage from 220 to 110. There is a rather long in the tooth 3.3K 1/2 watt resistor in there. I measured it in circuit at 3.5K. I wonder if I played around with the value of this resistor to bring the speed down. Perhaps start out with a 4K & see what I get.
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Old 7th December 2017, 06:47 PM   #2523
kevinkr is offline kevinkr  United States
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Restoring and Improving A Thorens TD-124 MKII
That resistor is actually 33K (orange orange orange plus gold [5%] or silver [10%] tolerance band if present) and is the current limiting resistor for the neon lamp.

It sounds like the magnet is a bit weak, but how close is it to the stepped pulley? As long as it does not hit the pulley you can place as close as necessary and should be OK. (Mine is about .15 inches from the pulley currently running on 117V 60Hz sine wave source)

Possibly you could remag it, but I currently know of no one who does this, seems there might be a market for a replacement magnet.

I am not sure the eddy current brake would work effectively with the magnets on the inside.

I posted the schematics for the motor and lamp connections in this thread long ago.
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Old 7th December 2017, 07:35 PM   #2524
volken is offline volken  Netherlands
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Quote:
Originally Posted by kleppermaster View Post
Update: 12/7/2017

OK, today I tore the table down and re-lubed the motor bearings, idler wheel and stepped speed pulley with 3-in-1 electric motor oil.<snip>
Are you also in possession of a rpm meter so you can measure the speed of the motor. I can measure your magnet and check it .
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Old 7th December 2017, 10:31 PM   #2525
kleppermaster is offline kleppermaster
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Originally Posted by kevinkr View Post
That resistor is actually 33K (orange orange orange plus gold [5%] or silver [10%] tolerance band if present) and is the current limiting resistor for the neon lamp. <snip>
Thanks you are correct about the resistor. My short term memory is pretty poor. It is an Orange orange orange silver.

My magnet is much closer than 0.150 In. I gapped it by placing a home depot receipt between the magnet and the stepped pulley. Loosened the magnet and scooted it up against the receipt then locked it down again. I estimate the gap at less than 0.005 in.
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Old 8th December 2017, 02:46 PM   #2526
kevinkr is offline kevinkr  United States
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Restoring and Improving A Thorens TD-124 MKII
That definitely sounds like a bad magnet. I have run across a number of ones of varying strength. I'm fortunate that the ones I have are all good. I actually encountered one that retained zero magnetism, and I have no clue how that could be.
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Old 8th December 2017, 09:28 PM   #2527
kleppermaster is offline kleppermaster
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I've been researching the magnet problem all day so far. Here is what I have and haven't come with.

I tested the strength of my magnet by lifting a transformer and clipping weight to the wires until it broke free of the magnet. The total that was held was then weighed on a digital postal scale. It looks like my magnet lifts about 3 pounds +/- 3 oz.

I looked up sources for replacement magnets and found nothing that would both fit and listed the lifting strength.

I looked for instructions on how to re-magnitize my magnet and am not yet satisfied I know the best way to do it. The easiest to find sites are:

A science site
How to Recharge a Horseshoe Magnet | Sciencing

that describes how to re-magnitize a horseshoe magnet using something called an "Electromagnetic Charger". They also say one can DIY one, but give no instructions. There are no pics on this site showing either the equipment used or the process. When I search for the electromagnetic charger I get all kinds of wireless battery charging devices. I don't think that is what they are talking about.

And a comercial site
Why are Magnets Shaped like Horseshoes?

That links to a youtube video and shoes how to demagnetize and remagnetize a magnet using Neodymium magnets.

I also found a forum (I didn't save it) where someone suggested remagnetizing using electromagnetism will result in a stronger magnet than the use of Neodymium magnets.

I also found a good source for Neodymium magnets.

SuperMagnetMan - Your Experienced Magnet Partner

The supermagnetman man also has lots of information and videos, but does not cover remagnitizing specifically. I tried contacting them, but no one was at home.

So here are my options:

Learn how to magnetize my magnet using the electromagnetic approach. (Preferred)

Buy some large 1/2 inch diameter neodynium cylinders and attempt to magnetize my magnet using them.

Buy some small neodynium discs, Grind the ends of my horseshoe magnet flat and epoxy them on. One neodymium disc .5 inches in diameter X .25 inches thick yealds 4.258 pounds of pull. 2 of them would give me close to twice that.

It would be nice to know the pulling strength of a brand new TD-124 eddy current magnet.
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Old 8th December 2017, 10:45 PM   #2528
kevinkr is offline kevinkr  United States
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Restoring and Improving A Thorens TD-124 MKII
If it is lifting 3 lbs I would say there is nothing wrong with the magnet, and you are having an issue common to MKIIs.

Are you using the correct side of the motor pulley? The larger diameter section of the pulley is for 50Hz.

The other thing is the belt, most are too thick and result in the table running a bit fast. Hanze HiFi has good belts for these tables.

Finally you might want to flush the main bearing and refill if there is any possibility of the previous oil mixing with the 20wt oil.
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Old 10th December 2017, 02:00 PM   #2529
volken is offline volken  Netherlands
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Quote:
Originally Posted by kleppermaster View Post
I've been researching the magnet problem all day so far. Here is what I have and haven't come with.<snip>

Here are some examples with the measured strenght the one with 100 pulls about 1 kg //2,2 lb.seems your magnet is ok.

WP_20171210_15_37_45_Rich 1.jpg
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Old 10th December 2017, 02:39 PM   #2530
kleppermaster is offline kleppermaster
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Thanks kevenkr solved my problem. Turns out the drive pulley on the motor was flipped to the 50Hz end. I flipped it over to the 60Hz end and it is keeping rock solid proper speed with about 0.100 gap between the magnet and the stepped pulley.

I'm verry pleased with the result and want to thank everyone on this site for their assistance.

Also I'm a little embarrassed I didn't catch this on my own. I pride myself on my mechanical skill. I'm surprised I missed this.
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