the Garrard 301 plater is concaved.

The original platter was not turned on a lathe. It was cast and then spun balanced with drilling of the heavier spots. I wish the chassis was also cast-but it was stamped. There is lots of literature available on this. EW Mortimer's book on the history of Garrard is a good start. 

everything I ready prior to my posting said it was a design feature, I was just surprised to find it in a table designed in the 50's.  The old Garrard's were better designed then I originally thought, well at least included some modern thinking. 

My head is gong to explode. Google Art Dudley and Thorens and Garrard and read his essays. Don't believe Art Dudley, google Ken Shindo and Audio Note and Garrard. The Thorens TD124 and Garrard 301 were designed and built with a level of precision and craftsmanship and engineering that remains unmatched to the present day. Both were built to be used in the broadcast industry where it was common to run the decks 24/7 for months at a time. You apparently have a 301 so did you not do any research or listening comparisons before buying? Both do have their minor challenges. The TD124 platter sits low in the chassis and can create challenges getting a modern arm low enough. The Garrards require a plinth that is massive and arguably "tuned" to cancel out motor noise. 

Of course I read quite a bit about the Garrard tables and never came across anything about the plinth being concave. really I posted this for some of us that didn't know but also as a funny post of my set up mistake, as human we all do them from time to time. If you can not laugh at your self you've had a miserable life IMO. 

I built my Garrard set up over a year. Sort of fell into a one owner 301 late grease bearing table. When the original owner lost his vision he decided to sell his table to a good friend of mine who also owns a vintage audio shop.  I walked in one day asked him about Garrard's after reading a few reviews one was Art's build, I was considering building up a table. That's when he pulled out this one owner table that he had just picked up that day. It was in very good original owner and condition, owned and maintained by a meticulous machinist.  

So I bought it on the spot, $2000 for the table. A year later I was up and running with a custom Bamboo Plinth and Jelco 750L arm. I was coming from an Oracle Delphi mk4 and the improvement in many areas was immediate. I'm Happy with the results even if its still an ongoing project, adding a new arm board for a second arm and footer system. 

They are great tables and I get why people like them, even if its a bit of work in the end its worth it.