THD BiValve 30 Class-A 30-Watt Tube Guitar Head

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As the name would suggest, the BiValve-30 amplifier head is a 30-watt amplifier with two output valves. It was released by THD in 2002. Like the UniValve, the BiValve-30's cathode-biasing allows it to adjust to individual tubes automatically. It is one of only a very few parallel-single-ended tube guitar amplifiers ever produced, and is the only one whose output transformer has separate primary windings for each power tube, accomplishing the unique feat of magnetically merging the outputs of the two power tubes—even if they are of dissimilar types—instead of simply connecting the plates of the two power tubes to a single primary winding to sum their outputs—which requires that the two tubes be of the same type. It, too, has a chemically-etched stainless steel faceplate, although THD chose a marine theme for the BiValve-30. Also, the BiValve-30 uses screen printing on the faceplate in addition to etching. In 2002, the BiValve-30 received a “Guitarist Choice” award from Guitarist Magazine, after being rated a 4.5 out of 5 possible stars. In that test, the BiValve-30 was given a slightly lower score in the “value for money” category, and the accompanying written review stated: “…definitely an amp for the well-heeled purist”.