Like the UniValve, the THD BiValve Rack-mounted Guitar Amp Head is a single-ended pure Class A design. However, it has two output valves that are wired in parallel and combined through a special output transformer to deliver up to around 30 watts. You can use almost any output valve you like without touching any kind of bias adjustment, and get this: in the BiValve you can use them in any combination as well. Combined with the capability to take almost any preamp valve, this makes the BiValve even more of an amp-tweaker's dream than its predecessor. Because there's such a wide range of tone available, you create your own style.The BiValve Rack mount amplifier head sits in the same compact pressed steel chassis as the UniValve and, except for the extra valve and control plate, it looks almost identical. Glasgow artist Charles Rennie Mackintosh inspired the UniValve's acid-etched control plate; this time round THD have gone for a marine theme, with an intricate diamond scale design. The control markings are screen printed, which makes them easier to see.Underneath the perforated steel lid there's a larger pair of transformers to handle the increased output, and inside there are two ultra-thick PCBs: one for the power supply and one for the audio. The four valve bases are bolted to the chassis and secured by locking nuts, with hi-fi style internal baffle plates to cut down on radiated hum. The standard of construction is absolutely top class. THD are based in Seattle, which is also hometown to Boeing, and most of the BiValve's heavy fabrication work is contracted out to local specialist companies who service the aircraft industry.The front panel looks deceptively simple. Working from the left, there's a pair of input jacks labeled "more" and "less", followed by a treble cut switch then rotary controls for volume, treble, bass and what THD call "Attitude". It's not a fancy name for a presence control - there'

The BiValve is a single-ended pure Class A design. However, it has two output valves which are wired in parallel and combined through a special output transformer to deliver up to around 30 watts. You can use almost any output valve you like without touching any kind of bias adjustment, and get this: in the BiValve you can use them in any combination as well.

This THD amp is a 30W, 1x12 combo version of the THD BiValve-30 Class A Amplifier Head which has 2 output tubes wired in parallel and combined through a special output transformer to deliver up to 30W. It accepts almost any type of output or preamp tube without bias adjustment—even in combination—for an astonishingly wide range of tone available for nearly any style of guitar playing. The amplifier's construction is absolutely top class, as you would expect for any handmade amplifier.Underneath its large, perforated steel lid you'll find large transformers and hi-fi style internal baffle plates to cut down on hum, as well as the tube sockets. On its front panel is a pair of input jacks labeled More and Less, followed by a Cut switch (high-cut filter), Volume, Treble, Bass, and Attitude (driver tube response control). In the center is a light bulb that glows as the amp distorts with a small switch to turn it off, a control for the THD BiValve-30's built-in Hot Plate (output attenuator), and a defeat switch for the Hot Plate.The THD BiValve-30 amp sports an acid-etched control plate with a delicate marine theme inspired by Glasgow artist Charles Rennie Mackintosh.

This model of Yellow Jackets® converter, the YJUni TRIODE, is a simple pin-converting adapter for use in most amplifiers which use 6V6 output tubes or other similar based tubes such as the 6F6, 6G6, 6K6, 6Y6, etc. All Yellow Jackets® converters come with JJ Brand EL84/6BQ5 vacuum tubes. * Converts pin configuration from 9-pin to 8-pin to allow certain 6V6, 6K6 and similar low-voltage circuits to use EL84 tubes. * One year limited warranty on converter. * Safe for all common amplifiers and transformers. * Great for adapting tube-testers to test EL84 tubes. * Perfect for THD UniValve, BiValve-30 and Flexi-50 amplifiers.Does not drop power

This model of Yellow Jackets® converter, the YJUni, is a simple pin-converting adapter for use in most amplifiers which use 6V6 output tubes or other similar based tubes such as the 6F6, 6G6, 6K6, 6Y6, etc. All Yellow Jackets® converters come with JJ Brand EL84/6BQ5 vacuum tubes. * Converts pin configuration from 9-pin to 8-pin to allow certain 6V6, 6K6 and similar low-voltage circuits to use EL84 tubes. * One year limited warranty on converter. * Safe for all common amplifiers and transformers. * Great for adapting tube-testers to test EL84 tubes. * Perfect for THD UniValve, BiValve-30 and Flexi-50 amplifiers.Does not drop power