ARC like some other equipment makers purchases lots of tubes for their equipment. They will tell you that the tubes they use and sell are only the finest and have been tested for everything under the sun, then they will charge you 3 times as much as if you purchase from an independent tube dealer. Let me recommend Kevin Deal of Upscale Audio to you. He is very knowledgable about tubes and has a fine reputation. He also prides himself on selling only high quality tubes. He also sells audio equipment. Go to his web site:
http://www.upscaleaudio.com/view_category.asp?cat=38
http://www.upscaleaudio.com/view_category.asp?cat=38