Audio Research Ref 5 preamp

say I want to tube roll the stock 6550c tube. I have a Tung Sol 6550, is it okay if I drop that in? I just want to make sure because I don't know what 6550c means in comparison to 6550. Also, there hasn't been any post, buzz or reviews on this preamp lately. Any owner impressions to add?

yeah, I have the American version. I originally bought them for extra tube for a Cayin KT 88 (was using 6550s in place of the 88s). Okay, then I will drop the Tung Sol in the ARC REF 5. Thanks for the helpful response.

No, I stand corrected. My Tung-sol 6550s were made in Russia. Even so, they sure sound pretty good to my ears.