THD Electronics BIV30R-BLK BiValve-30, Rack-Mounted, Black 120V Make all of your Tone Dreams come true with the THD BiValve-30. Great headroom, shimmery highs and tight bass characterize this little monster. Like the UniValve, the BiValve-30 is a Single-Ended Class A amplifier head but with two output tubes that can be switched at will among many octal-based power tubes including 6L6, EL34, 6550, KT90, KT88, KT77 and KT66, for different tones without re-biasing the amp All parts are black powder-coated steel. Provides ample ventilation for the preamp and power tubes. Hand-built in Seattle, WA.