$510.00 for an Aluminum cover for the ARC Ref. 10?

I your Ref 10 is under warranty it should be covered. Talk to your dealer. The top of my Ref 5se had a slight warp from heat. I complained to my dealer and he asked if I would prefer a metal cover instead. I told him a replacement poly cover seemed pointless. ARC sent me a replacement metal cover under warranty. My Ref 5se was almost a year old at that point.

Copy it, start making and sell for half price.

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ARC figures that if you could afford a $30k preamp, to ding you $500 for a lid, you probably wouldn't notice.
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Its true.

Expensive stuff usually means expensive parts and support, just like with cars.

Same laws of physics apply to all luxury items.

They know we can't do without and everything must be perfect. There is no escape.

Tell them you can't afford it and your willing to sell the thing and take an even bigger loss just on principle.

Maybe they'll cut a deal to help keep a customer happy.

I own an ARC pre-amp and like it and ARC a lot. I've bought replacement tubes from ARC. They were not cheap (almost as much as your lid) but of good quality and have lasted pretty long (jinx...not I hope). So I was happy.

First I believe the Ref 10 has 2 tops not 1.

The Tops should be covered by warranty if the unit is less than 3 years old.

If it is over 3 years old then call the ARC service department and complain. It is a design flaw and ARC knows it. They will likely give you a discount on the metal tops.