$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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