Swapping Platters on Thorens 124

So I got the Decca and used it with the magnetic platter and an 5mm achromat and there's no problem at all (I have an aluminum top platter and that may help too.) 

That's very interesting! Thanks for the info. Looking forward to giving it a try. 

I have a MKI with the Woodsong hub replacement and a Tenuto mat. I have no problems with my Decca’s or SPU’s. That said I didn’t have a problem before I had the thick Tenuto mat either. I know these issues must be based on some type of genuine historical mismatches, but I’ve never had a problem. Just make sure you measure VTF from on top of the platter. I do notice VTF increases on top of the platter vs outside of it, but this hasn’t been detrimental to my ears. 

Thanks @dhcod. I too use London's, and am myself interested in getting TD-124. Keep us appraised, ay?

Yes, that is the case. I have an aluminum top platter which is a great upgrade but still use the iron bottom platter. I've just purchased a Woodsong Audio thingy that replaces the pop up 45 mechanism so any mat will work and I bought an Achromat to hopefully raise everything high enough so the Decca will work. Fingers crossed. 

I have been told (by Art Dudley) it is the sub-platter on the Mk.1 that is ferrous, not the top platter. True or false?

Anticipating. I haven't wanted to try it because I don't want to risk damaging the Decca. I also use a Herbie's mat with mine and it's super thin. I was able to grab a non magnetic platter for cheap so I thought I'd give it a try before I invested in a new aftermarket one. 

What mat do you recommend that could block the magnetism if I want to keep the aluminum top platter?

Thanks for responding!

Are you having a problem with the London Decca cartridge and the TD-124 iron platter, or are you anticipating a problem?

I ask because I am using a London Decca Super Gold with my TD-124 Mk I and it works fine.  I am also using several SPU cartridges without any problems.  But if you ARE experiencing a problem I can offer a couple of suggestions:

1- before you replace the platter, try replacing the Thorens rubber mat.  There are several drop-in replacements that will allow you to retain the aluminum outer platter shell.  If you want/need a thicker mat you can remove the platter shell and fit a cork/delrin/leather/copper "mat."

2- If you want to replace the platter I suggest that you use something other than the Mk II aluminum platter.  I am not a fan for various reasons; basically IMO it does not sound as good as other alternatives.  You will be better served by a stainless steel or brass replacement platter.  I know that they are more expensive (but not that much more expensive).  Welcome to the joys of mid-century idler wheel ownership.