Absolutely awesome head! It is the SVT-HD, affectionately known as the "skunk works" SVT, and is the real deal. I owned number 65 of 500. Without a doubt, the best sounding and most bullet proof bass amp I ever had the pleasure of owning.
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In response to the post: "Old blues players use to slice their speaker cones with razor blades to get some fuzz sound. They really liked that."
Search for SVT-HD. These were hand built by SLM after buying the company from MTI in the 80s. Only 500 were made with the remaining parts from the sale and they were the last of the 2 channel SVTs until the SVT-VR. A few years after this run SLM introduced the SVT-CL. The HD series are very highly regarded among SVTs and considered next best to a vintage amp by some.